<feed xmlns='http://www.w3.org/2005/Atom'>
<title>linux/tools/arch/powerpc/include, branch v5.8</title>
<subtitle>Mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
</subtitle>
<id>https://git.shady.money/linux/atom?h=v5.8</id>
<link rel='self' href='https://git.shady.money/linux/atom?h=v5.8'/>
<link rel='alternate' type='text/html' href='https://git.shady.money/linux/'/>
<updated>2019-12-02T15:54:13Z</updated>
<entry>
<title>tools headers kvm: Sync kvm headers with the kernel sources</title>
<updated>2019-12-02T15:54:13Z</updated>
<author>
<name>Arnaldo Carvalho de Melo</name>
<email>acme@redhat.com</email>
</author>
<published>2019-12-02T15:44:24Z</published>
<link rel='alternate' type='text/html' href='https://git.shady.money/linux/commit/?id=1fc3d0ee242de68267769afcaf5520439de42f64'/>
<id>urn:sha1:1fc3d0ee242de68267769afcaf5520439de42f64</id>
<content type='text'>
To pick up the changes from:

  14edff88315a Merge tag 'kvmarm-5.5' of git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm into HEAD
  a4b28f5c6798 Merge remote-tracking branch 'kvmarm/kvm-arm64/stolen-time' into kvmarm-master/next
  58772e9a3db7 ("KVM: arm64: Provide VCPU attributes for stolen time")
  da345174ceca ("KVM: arm/arm64: Allow user injection of external data aborts")
  c726200dd106 ("KVM: arm/arm64: Allow reporting non-ISV data aborts to userspace")
  efe5ddcae496 ("KVM: PPC: Book3S HV: XIVE: Allow userspace to set the # of VPs")

No tools changes are caused by this, as the only defines so far used
from these files are for syscall arg pretty printing are:

  $ grep KVM tools/perf/trace/beauty/*.sh
  tools/perf/trace/beauty/kvm_ioctl.sh:regex='^#[[:space:]]*define[[:space:]]+KVM_(\w+)[[:space:]]+_IO[RW]*\([[:space:]]*KVMIO[[:space:]]*,[[:space:]]*(0x[[:xdigit:]]+).*'
  $

Some are also include by:

  tools/perf/arch/x86/util/kvm-stat.c
  tools/perf/arch/powerpc/util/kvm-stat.c

This addresses these tools/perf build warnings:

  Warning: Kernel ABI header at 'tools/include/uapi/linux/kvm.h' differs from latest version at 'include/uapi/linux/kvm.h'
  diff -u tools/include/uapi/linux/kvm.h include/uapi/linux/kvm.h
  Warning: Kernel ABI header at 'tools/arch/powerpc/include/uapi/asm/kvm.h' differs from latest version at 'arch/powerpc/include/uapi/asm/kvm.h'
  diff -u tools/arch/powerpc/include/uapi/asm/kvm.h arch/powerpc/include/uapi/asm/kvm.h
  Warning: Kernel ABI header at 'tools/arch/arm/include/uapi/asm/kvm.h' differs from latest version at 'arch/arm/include/uapi/asm/kvm.h'
  diff -u tools/arch/arm/include/uapi/asm/kvm.h arch/arm/include/uapi/asm/kvm.h
  Warning: Kernel ABI header at 'tools/arch/arm64/include/uapi/asm/kvm.h' differs from latest version at 'arch/arm64/include/uapi/asm/kvm.h'
  diff -u tools/arch/arm64/include/uapi/asm/kvm.h arch/arm64/include/uapi/asm/kvm.h

Cc: Adrian Hunter &lt;adrian.hunter@intel.com&gt;
Cc: Christoffer Dall &lt;christoffer.dall@arm.com&gt;
Cc: Fabiano Rosas &lt;farosas@linux.ibm.com&gt;
Cc: Greg Kurz &lt;groug@kaod.org&gt;
Cc: Jiri Olsa &lt;jolsa@kernel.org&gt;
Cc: Marc Zyngier &lt;maz@kernel.org&gt;
Cc: Namhyung Kim &lt;namhyung@kernel.org&gt;
Cc: Paul Mackerras &lt;paulus@ozlabs.org&gt;
Cc: Steven Price &lt;steven.price@arm.com&gt;
Link: https://lkml.kernel.org/n/tip-qrjdudhq25mk5bfnhveofbm4@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo &lt;acme@redhat.com&gt;
</content>
</entry>
<entry>
<title>tools headers UAPI: Update tools's copy of mman.h headers</title>
<updated>2019-07-29T12:02:58Z</updated>
<author>
<name>Arnaldo Carvalho de Melo</name>
<email>acme@redhat.com</email>
</author>
<published>2019-07-26T15:49:00Z</published>
<link rel='alternate' type='text/html' href='https://git.shady.money/linux/commit/?id=b830f94f7303a49d509d5b1bb34ecb2e648b23c4'/>
<id>urn:sha1:b830f94f7303a49d509d5b1bb34ecb2e648b23c4</id>
<content type='text'>
To pick up the changes from:

  8aa3c927ec10 ("mm/mmap: move common defines to mman-common.h")
  22fcea6f85f2 ("mm: move MAP_SYNC to asm-generic/mman-common.h")
  0bf5f9492389 ("mm: fix the MAP_UNINITIALIZED flag")

To address the following perf build warnings:

  Warning: Kernel ABI header at 'tools/include/uapi/asm-generic/mman-common.h' differs from latest version at 'include/uapi/asm-generic/mman-common.h'
  diff -u tools/include/uapi/asm-generic/mman-common.h include/uapi/asm-generic/mman-common.h
  Warning: Kernel ABI header at 'tools/include/uapi/asm-generic/mman.h' differs from latest version at 'include/uapi/asm-generic/mman.h'
  diff -u tools/include/uapi/asm-generic/mman.h include/uapi/asm-generic/mman.h

That ends up just moving a bit the auto-generated code-&gt;string tables:

  $ tools/perf/trace/beauty/mmap_flags.sh &gt; before
  $ cp include/uapi/asm-generic/mman.h tools/include/uapi/asm-generic/mman.h
  $ cp include/uapi/asm-generic/mman-common.h tools/include/uapi/asm-generic/mman-common.h
  $ tools/perf/trace/beauty/mmap_flags.sh &gt; after
  $ diff -u before after
  --- before 2019-07-26 12:45:02.948335904 -0300
  +++ after 2019-07-26 12:48:05.342893539 -0300
  @@ -4,15 +4,15 @@
          [ilog2(0x02) + 1] = "PRIVATE",
          [ilog2(0x10) + 1] = "FIXED",
          [ilog2(0x20) + 1] = "ANONYMOUS",
  +       [ilog2(0x008000) + 1] = "POPULATE",
  +       [ilog2(0x010000) + 1] = "NONBLOCK",
  +       [ilog2(0x020000) + 1] = "STACK",
  +       [ilog2(0x040000) + 1] = "HUGETLB",
  +       [ilog2(0x080000) + 1] = "SYNC",
          [ilog2(0x100000) + 1] = "FIXED_NOREPLACE",
          [ilog2(0x0100) + 1] = "GROWSDOWN",
          [ilog2(0x0800) + 1] = "DENYWRITE",
          [ilog2(0x1000) + 1] = "EXECUTABLE",
          [ilog2(0x2000) + 1] = "LOCKED",
          [ilog2(0x4000) + 1] = "NORESERVE",
  -       [ilog2(0x8000) + 1] = "POPULATE",
  -       [ilog2(0x10000) + 1] = "NONBLOCK",
  -       [ilog2(0x20000) + 1] = "STACK",
  -       [ilog2(0x40000) + 1] = "HUGETLB",
  -       [ilog2(0x80000) + 1] = "SYNC",
   };
  $

Cc: Adrian Hunter &lt;adrian.hunter@intel.com&gt;
Cc: Aneesh Kumar K.V &lt;aneesh.kumar@linux.ibm.com&gt;
Cc: Christoph Hellwig &lt;hch@lst.de&gt;
Cc: Jiri Olsa &lt;jolsa@kernel.org&gt;
Cc: Luis Cláudio Gonçalves &lt;lclaudio@redhat.com&gt;
Cc: Namhyung Kim &lt;namhyung@kernel.org&gt;
Link: https://lkml.kernel.org/n/tip-fzqvzni9megaurmsp0k4vy27@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo &lt;acme@redhat.com&gt;
</content>
</entry>
<entry>
<title>tools headers UAPI: Sync kvm.h headers with the kernel sources</title>
<updated>2019-05-28T12:52:23Z</updated>
<author>
<name>Arnaldo Carvalho de Melo</name>
<email>acme@redhat.com</email>
</author>
<published>2019-05-24T17:04:15Z</published>
<link rel='alternate' type='text/html' href='https://git.shady.money/linux/commit/?id=a7350998a25ac10cdca5b33dee1d343a74debbfe'/>
<id>urn:sha1:a7350998a25ac10cdca5b33dee1d343a74debbfe</id>
<content type='text'>
  dd53f6102c30 ("Merge tag 'kvmarm-for-v5.2' of git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm into HEAD")
  59c5c58c5b93 ("Merge tag 'kvm-ppc-next-5.2-2' of git://git.kernel.org/pub/scm/linux/kernel/git/paulus/powerpc into HEAD")
  d7547c55cbe7 ("KVM: Introduce KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2")
  6520ca64cde7 ("KVM: PPC: Book3S HV: XIVE: Add a mapping for the source ESB pages")
  39e9af3de5ca ("KVM: PPC: Book3S HV: XIVE: Add a TIMA mapping")
  e4945b9da52b ("KVM: PPC: Book3S HV: XIVE: Add get/set accessors for the VP XIVE state")
  e6714bd1671d ("KVM: PPC: Book3S HV: XIVE: Add a control to dirty the XIVE EQ pages")
  7b46b6169ab8 ("KVM: PPC: Book3S HV: XIVE: Add a control to sync the sources")
  5ca806474859 ("KVM: PPC: Book3S HV: XIVE: Add a global reset control")
  13ce3297c576 ("KVM: PPC: Book3S HV: XIVE: Add controls for the EQ configuration")
  e8676ce50e22 ("KVM: PPC: Book3S HV: XIVE: Add a control to configure a source")
  4131f83c3d64 ("KVM: PPC: Book3S HV: XIVE: add a control to initialize a source")
  eacc56bb9de3 ("KVM: PPC: Book3S HV: XIVE: Introduce a new capability KVM_CAP_PPC_IRQ_XIVE")
  90c73795afa2 ("KVM: PPC: Book3S HV: Add a new KVM device for the XIVE native exploitation mode")
  4f45b90e1c03 ("KVM: s390: add deflate conversion facilty to cpu model")
  a243c16d18be ("KVM: arm64: Add capability to advertise ptrauth for guest")
  a22fa321d13b ("KVM: arm64: Add userspace flag to enable pointer authentication")
  4bd774e57b29 ("KVM: arm64/sve: Simplify KVM_REG_ARM64_SVE_VLS array sizing")
  8ae6efdde451 ("KVM: arm64/sve: Clean up UAPI register ID definitions")
  173aec2d5a9f ("KVM: s390: add enhanced sort facilty to cpu model")
  555f3d03e7fb ("KVM: arm64: Add a capability to advertise SVE support")
  9033bba4b535 ("KVM: arm64/sve: Add pseudo-register for the guest's vector lengths")
  7dd32a0d0103 ("KVM: arm/arm64: Add KVM_ARM_VCPU_FINALIZE ioctl")
  e1c9c98345b3 ("KVM: arm64/sve: Add SVE support to register access ioctl interface")
  2b953ea34812 ("KVM: Allow 2048-bit register access via ioctl interface")

None entails changes in tooling, the closest to that were some new arch
specific ioctls, that are still not handled by the tools/perf/trace/beauty/
library, that needs to create per-arch tables to convert ioctl cmd-&gt;string (and
back).

From a quick look the arch specific kvm-stat.c files at:

  $ ls -1 tools/perf/arch/*/util/kvm-stat.c
  tools/perf/arch/powerpc/util/kvm-stat.c
  tools/perf/arch/s390/util/kvm-stat.c
  tools/perf/arch/x86/util/kvm-stat.c
  $

Are not affected.

This silences these perf building warnings:

  Warning: Kernel ABI header at 'tools/include/uapi/linux/kvm.h' differs from latest version at 'include/uapi/linux/kvm.h'
  diff -u tools/include/uapi/linux/kvm.h include/uapi/linux/kvm.h
  Warning: Kernel ABI header at 'tools/arch/powerpc/include/uapi/asm/kvm.h' differs from latest version at 'arch/powerpc/include/uapi/asm/kvm.h'
  diff -u tools/arch/powerpc/include/uapi/asm/kvm.h arch/powerpc/include/uapi/asm/kvm.h
  Warning: Kernel ABI header at 'tools/arch/s390/include/uapi/asm/kvm.h' differs from latest version at 'arch/s390/include/uapi/asm/kvm.h'
  diff -u tools/arch/s390/include/uapi/asm/kvm.h arch/s390/include/uapi/asm/kvm.h
  Warning: Kernel ABI header at 'tools/arch/arm64/include/uapi/asm/kvm.h' differs from latest version at 'arch/arm64/include/uapi/asm/kvm.h'
  diff -u tools/arch/arm64/include/uapi/asm/kvm.h arch/arm64/include/uapi/asm/kvm.h

Cc: Adrian Hunter &lt;adrian.hunter@intel.com&gt;
Cc: Amit Daniel Kachhap &lt;amit.kachhap@arm.com&gt;
Cc: Brendan Gregg &lt;brendan.d.gregg@gmail.com&gt;
Cc: Cédric Le Goater &lt;clg@kaod.org&gt;
Cc: Christian Borntraeger &lt;borntraeger@de.ibm.com&gt;
Cc: Dave Martin &lt;Dave.Martin@arm.com&gt;
Cc: Jiri Olsa &lt;jolsa@kernel.org&gt;
Cc: Luis Cláudio Gonçalves &lt;lclaudio@redhat.com&gt;
Cc: Marc Zyngier &lt;marc.zyngier@arm.com&gt;
Cc: Namhyung Kim &lt;namhyung@kernel.org&gt;
Cc: Paolo Bonzini &lt;pbonzini@redhat.com&gt;
Cc: Paul Mackerras &lt;paulus@ozlabs.org&gt;
Cc: Peter Xu &lt;peterx@redhat.com&gt;
Link: https://lkml.kernel.org/n/tip-3msmqjenlmb7eygcdnmlqaq1@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo &lt;acme@redhat.com&gt;
</content>
</entry>
<entry>
<title>tools headers uapi: Sync powerpc's asm/kvm.h copy with the kernel sources</title>
<updated>2019-03-28T17:41:21Z</updated>
<author>
<name>Arnaldo Carvalho de Melo</name>
<email>acme@redhat.com</email>
</author>
<published>2019-03-26T16:45:58Z</published>
<link rel='alternate' type='text/html' href='https://git.shady.money/linux/commit/?id=707c373c846cf6e27a47a2c093d243a35c691b62'/>
<id>urn:sha1:707c373c846cf6e27a47a2c093d243a35c691b62</id>
<content type='text'>
To pick up the changes in:

  2b57ecd0208f ("KVM: PPC: Book3S: Add count cache flush parameters to kvmppc_get_cpu_char()")

That don't cause any changes in the tools.

This silences this perf build warning:

  Warning: Kernel ABI header at 'tools/arch/powerpc/include/uapi/asm/kvm.h' differs from latest version at 'arch/powerpc/include/uapi/asm/kvm.h'
  diff -u tools/arch/powerpc/include/uapi/asm/kvm.h arch/powerpc/include/uapi/asm/kvm.h

Cc: Adrian Hunter &lt;adrian.hunter@intel.com&gt;
Cc: Jiri Olsa &lt;jolsa@kernel.org&gt;
Cc: Namhyung Kim &lt;namhyung@kernel.org&gt;
Cc: Paul Mackerras &lt;paulus@ozlabs.org&gt;
Cc: Suraj Jitindar Singh &lt;sjitindarsingh@gmail.com&gt;
Link: https://lkml.kernel.org/n/tip-4pb7ywp9536hub2pnj4hu6i4@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo &lt;acme@redhat.com&gt;
</content>
</entry>
<entry>
<title>Merge tag 'powerpc-5.0-3' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux</title>
<updated>2019-01-18T17:55:42Z</updated>
<author>
<name>Linus Torvalds</name>
<email>torvalds@linux-foundation.org</email>
</author>
<published>2019-01-18T17:55:42Z</published>
<link rel='alternate' type='text/html' href='https://git.shady.money/linux/commit/?id=c5b709804ed7d36c45b5efa170d9e3ea8c29b865'/>
<id>urn:sha1:c5b709804ed7d36c45b5efa170d9e3ea8c29b865</id>
<content type='text'>
Pull powerpc fixes from Michael Ellerman:
 "A couple of weeks of fixes.

  There's one fix for an oops on Power9 machines with Open CAPI
  adapters.

  And a fix for probable memory corruption in some of the new NPU code,
  caught by smatch though and not seen in the wild.

  Plus a few other minor fixes.

  There's one non-fix which is the perf_regs change. That was sent
  during the merge window but I accidentally only merged the first of
  two patches in the series. It's been in linux-next so hopefully
  doesn't conflict with anything in acme's tree.

  Thanks to: Alexey Kardashevskiy, Andrew Donnellan, Breno Leitao,
  Christian Lamparter, Christophe Leroy, Dan Carpenter, Frederic Barrat,
  Greg Kurz, Jason A. Donenfeld, Madhavan Srinivasan"

* tag 'powerpc-5.0-3' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux:
  powerpc/syscalls: Fix syscall tracing
  powerpc/pseries: Fix build break due to pnv_npu2_init()
  powerpc/4xx/ocm: Fix fix for phys_addr_t printf warnings
  powerpc/powernv/npu: Fix oops in pnv_try_setup_npu_table_group()
  powerpc/tm: Limit TM code inside PPC_TRANSACTIONAL_MEM
  powerpc/8xx: fix setting of pagetable for Abatron BDI debug tool.
  powerpc/powernv/npu: Allocate enough memory in pnv_try_setup_npu_table_group()
  powerpc/perf: Update perf_regs structure to include MMCRA
</content>
</entry>
<entry>
<title>tools headers powerpc: Remove unistd.h</title>
<updated>2019-01-10T13:42:08Z</updated>
<author>
<name>Ravi Bangoria</name>
<email>ravi.bangoria@linux.ibm.com</email>
</author>
<published>2019-01-10T09:49:36Z</published>
<link rel='alternate' type='text/html' href='https://git.shady.money/linux/commit/?id=15c03092a9fbcdd041f58e5f832bf76c21c42e6a'/>
<id>urn:sha1:15c03092a9fbcdd041f58e5f832bf76c21c42e6a</id>
<content type='text'>
We use syscall.tbl to generate system call table on powerpc.

The unistd.h copy is no longer required now. Remove it.

Signed-off-by: Ravi Bangoria &lt;ravi.bangoria@linux.ibm.com&gt;
Cc: Jiri Olsa &lt;jolsa@redhat.com&gt;
Cc: Michael Ellerman &lt;mpe@ellerman.id.au&gt;
Cc: Namhyung Kim &lt;namhyung@kernel.org&gt;
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/20190110094936.3132-2-ravi.bangoria@linux.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo &lt;acme@redhat.com&gt;
</content>
</entry>
<entry>
<title>powerpc/perf: Update perf_regs structure to include MMCRA</title>
<updated>2019-01-08T08:22:47Z</updated>
<author>
<name>Madhavan Srinivasan</name>
<email>maddy@linux.vnet.ibm.com</email>
</author>
<published>2018-12-09T09:25:36Z</published>
<link rel='alternate' type='text/html' href='https://git.shady.money/linux/commit/?id=6529870cb0323823f49b3e95d1760383910f96cd'/>
<id>urn:sha1:6529870cb0323823f49b3e95d1760383910f96cd</id>
<content type='text'>
On each sample, Monitor Mode Control Register A (MMCRA) content is
saved in pt_regs. MMCRA does not have a entry as-is in the pt_regs but
instead, MMCRA content is saved in the "dsisr" register of pt_regs.

Patch adds another entry to the perf_regs structure to include the
"MMCRA" printing which internally maps to the "dsisr" of pt_regs.

It also check for the MMCRA availability in the platform and present
value accordingly

mpe: This was the 2nd patch in a series with commit 333804dc3b7a
("powerpc/perf: Update perf_regs structure to include SIER") but I
accidentally only merged the 1st patch, so merge this one now.

Signed-off-by: Madhavan Srinivasan &lt;maddy@linux.vnet.ibm.com&gt;
Signed-off-by: Michael Ellerman &lt;mpe@ellerman.id.au&gt;
</content>
</entry>
<entry>
<title>powerpc/perf: Update perf_regs structure to include SIER</title>
<updated>2018-12-20T09:53:11Z</updated>
<author>
<name>Madhavan Srinivasan</name>
<email>maddy@linux.vnet.ibm.com</email>
</author>
<published>2018-12-09T09:25:35Z</published>
<link rel='alternate' type='text/html' href='https://git.shady.money/linux/commit/?id=333804dc3b7a92158ab63a48febff0d8ef89ada3'/>
<id>urn:sha1:333804dc3b7a92158ab63a48febff0d8ef89ada3</id>
<content type='text'>
On each sample, Sample Instruction Event Register (SIER) content
is saved in pt_regs. SIER does not have a entry as-is in the pt_regs
but instead, SIER content is saved in the "dar" register of pt_regs.

Patch adds another entry to the perf_regs structure to include the "SIER"
printing which internally maps to the "dar" of pt_regs.

It also check for the SIER availability in the platform and present
value accordingly

Signed-off-by: Madhavan Srinivasan &lt;maddy@linux.vnet.ibm.com&gt;
Signed-off-by: Michael Ellerman &lt;mpe@ellerman.id.au&gt;
</content>
</entry>
<entry>
<title>tools headers: Sync the various kvm.h header copies</title>
<updated>2018-10-31T12:57:53Z</updated>
<author>
<name>Arnaldo Carvalho de Melo</name>
<email>acme@redhat.com</email>
</author>
<published>2018-10-30T20:01:46Z</published>
<link rel='alternate' type='text/html' href='https://git.shady.money/linux/commit/?id=827758129a0f84fbd0b2dda15e14a77a7604803d'/>
<id>urn:sha1:827758129a0f84fbd0b2dda15e14a77a7604803d</id>
<content type='text'>
For powerpc, s390, x86 and the main uapi linux/kvm.h header, none of
them entail changes in tooling.

Cc: Jiri Olsa &lt;jolsa@kernel.org&gt;
Cc: Namhyung Kim &lt;namhyung@kernel.org&gt;
Link: https://lkml.kernel.org/n/tip-avn7iy8f4tcm2y40sbsdk31m@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo &lt;acme@redhat.com&gt;
</content>
</entry>
<entry>
<title>tools, perf: add and use optimized ring_buffer_{read_head, write_tail} helpers</title>
<updated>2018-10-19T20:43:08Z</updated>
<author>
<name>Daniel Borkmann</name>
<email>daniel@iogearbox.net</email>
</author>
<published>2018-10-19T13:51:02Z</published>
<link rel='alternate' type='text/html' href='https://git.shady.money/linux/commit/?id=09d62154f61316f7e97eae3f31ef8770c7e4b386'/>
<id>urn:sha1:09d62154f61316f7e97eae3f31ef8770c7e4b386</id>
<content type='text'>
Currently, on x86-64, perf uses LFENCE and MFENCE (rmb() and mb(),
respectively) when processing events from the perf ring buffer which
is unnecessarily expensive as we can do more lightweight in particular
given this is critical fast-path in perf.

According to Peter rmb()/mb() were added back then via a94d342b9cb0
("tools/perf: Add required memory barriers") at a time where kernel
still supported chips that needed it, but nowadays support for these
has been ditched completely, therefore we can fix them up as well.

While for x86-64, replacing rmb() and mb() with smp_*() variants would
result in just a compiler barrier for the former and LOCK + ADD for
the latter (__sync_synchronize() uses slower MFENCE by the way), Peter
suggested we can use smp_{load_acquire,store_release}() instead for
architectures where its implementation doesn't resolve in slower smp_mb().
Thus, e.g. in x86-64 we would be able to avoid CPU barrier entirely due
to TSO. For architectures where the latter needs to use smp_mb() e.g.
on arm, we stick to cheaper smp_rmb() variant for fetching the head.

This work adds helpers ring_buffer_read_head() and ring_buffer_write_tail()
for tools infrastructure that either switches to smp_load_acquire() for
architectures where it is cheaper or uses READ_ONCE() + smp_rmb() barrier
for those where it's not in order to fetch the data_head from the perf
control page, and it uses smp_store_release() to write the data_tail.
Latter is smp_mb() + WRITE_ONCE() combination or a cheaper variant if
architecture allows for it. Those that rely on smp_rmb() and smp_mb() can
further improve performance in a follow up step by implementing the two
under tools/arch/*/include/asm/barrier.h such that they don't have to
fallback to rmb() and mb() in tools/include/asm/barrier.h.

Switch perf to use ring_buffer_read_head() and ring_buffer_write_tail()
so it can make use of the optimizations. Later, we convert libbpf as
well to use the same helpers.

Side note [0]: the topic has been raised of whether one could simply use
the C11 gcc builtins [1] for the smp_load_acquire() and smp_store_release()
instead:

  __atomic_load_n(ptr, __ATOMIC_ACQUIRE);
  __atomic_store_n(ptr, val, __ATOMIC_RELEASE);

Kernel and (presumably) tooling shipped along with the kernel has a
minimum requirement of being able to build with gcc-4.6 and the latter
does not have C11 builtins. While generally the C11 memory models don't
align with the kernel's, the C11 load-acquire and store-release alone
/could/ suffice, however. Issue is that this is implementation dependent
on how the load-acquire and store-release is done by the compiler and
the mapping of supported compilers must align to be compatible with the
kernel's implementation, and thus needs to be verified/tracked on a
case by case basis whether they match (unless an architecture uses them
also from kernel side). The implementations for smp_load_acquire() and
smp_store_release() in this patch have been adapted from the kernel side
ones to have a concrete and compatible mapping in place.

  [0] http://patchwork.ozlabs.org/patch/985422/
  [1] https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html

Signed-off-by: Daniel Borkmann &lt;daniel@iogearbox.net&gt;
Acked-by: Peter Zijlstra (Intel) &lt;peterz@infradead.org&gt;
Cc: "Paul E. McKenney" &lt;paulmck@linux.vnet.ibm.com&gt;
Cc: Will Deacon &lt;will.deacon@arm.com&gt;
Cc: Arnaldo Carvalho de Melo &lt;acme@redhat.com&gt;
Signed-off-by: Alexei Starovoitov &lt;ast@kernel.org&gt;
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