Go to file
Kan Liang 35d1ce6bec perf/x86/intel/ds: Fix x86_pmu_stop warning for large PEBS
A warning as below may be triggered when sampling with large PEBS.

[  410.411250] perf: interrupt took too long (72145 > 71975), lowering
kernel.perf_event_max_sample_rate to 2000
[  410.724923] ------------[ cut here ]------------
[  410.729822] WARNING: CPU: 0 PID: 16397 at arch/x86/events/core.c:1422
x86_pmu_stop+0x95/0xa0
[  410.933811]  x86_pmu_del+0x50/0x150
[  410.937304]  event_sched_out.isra.0+0xbc/0x210
[  410.941751]  group_sched_out.part.0+0x53/0xd0
[  410.946111]  ctx_sched_out+0x193/0x270
[  410.949862]  __perf_event_task_sched_out+0x32c/0x890
[  410.954827]  ? set_next_entity+0x98/0x2d0
[  410.958841]  __schedule+0x592/0x9c0
[  410.962332]  schedule+0x5f/0xd0
[  410.965477]  exit_to_usermode_loop+0x73/0x120
[  410.969837]  prepare_exit_to_usermode+0xcd/0xf0
[  410.974369]  ret_from_intr+0x2a/0x3a
[  410.977946] RIP: 0033:0x40123c
[  411.079661] ---[ end trace bc83adaea7bb664a ]---

In the non-overflow context, e.g., context switch, with large PEBS, perf
may stop an event twice. An example is below.

  //max_samples_per_tick is adjusted to 2
  //NMI is triggered
  intel_pmu_handle_irq()
     handle_pmi_common()
       drain_pebs()
         __intel_pmu_pebs_event()
           perf_event_overflow()
             __perf_event_account_interrupt()
               hwc->interrupts = 1
               return 0
  //A context switch happens right after the NMI.
  //In the same tick, the perf_throttled_seq is not changed.
  perf_event_task_sched_out()
     perf_pmu_sched_task()
       intel_pmu_drain_pebs_buffer()
         __intel_pmu_pebs_event()
           perf_event_overflow()
             __perf_event_account_interrupt()
               ++hwc->interrupts >= max_samples_per_tick
               return 1
           x86_pmu_stop();  # First stop
     perf_event_context_sched_out()
       task_ctx_sched_out()
         ctx_sched_out()
           event_sched_out()
             x86_pmu_del()
               x86_pmu_stop();  # Second stop and trigger the warning

Perf should only invoke the perf_event_overflow() in the overflow
context.

Current drain_pebs() is called from:
- handle_pmi_common()			-- overflow context
- intel_pmu_pebs_sched_task()		-- non-overflow context
- intel_pmu_pebs_disable()		-- non-overflow context
- intel_pmu_auto_reload_read()		-- possible overflow context
  With PERF_SAMPLE_READ + PERF_FORMAT_GROUP, the function may be
  invoked in the NMI handler. But, before calling the function, the
  PEBS buffer has already been drained. The __intel_pmu_pebs_event()
  will not be called in the possible overflow context.

To fix the issue, an indicator is required to distinguish between the
overflow context aka handle_pmi_common() and other cases.
The dummy regs pointer can be used as the indicator.

In the non-overflow context, perf should treat the last record the same
as other PEBS records, and doesn't invoke the generic overflow handler.

Fixes: 21509084f9 ("perf/x86/intel: Handle multiple records in the PEBS buffer")
Reported-by: Like Xu <like.xu@linux.intel.com>
Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Like Xu <like.xu@linux.intel.com>
Link: https://lkml.kernel.org/r/20200902210649.2743-1-kan.liang@linux.intel.com
2020-09-10 11:19:33 +02:00
Documentation Misc fixes and small updates all around the place: 2020-08-15 10:38:03 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch perf/x86/intel/ds: Fix x86_pmu_stop warning for large PEBS 2020-09-10 11:19:33 +02:00
block block-5.9-2020-08-14 2020-08-15 20:36:42 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2020-08-14 13:09:15 -07:00
drivers block-5.9-2020-08-14 2020-08-15 20:36:42 -07:00
fs io_uring-5.9-2020-08-15 2020-08-16 10:55:12 -07:00
include perf/x86/intel: Support per-thread RDPMC TopDown metrics 2020-08-18 16:34:37 +02:00
init OpenRISC updates for 5.9 2020-08-14 14:04:53 -07:00
ipc ipc/shm.c: remove the superfluous break 2020-08-12 10:58:02 -07:00
kernel perf/core: Add a new PERF_EV_CAP_SIBLING event capability 2020-08-18 16:34:36 +02:00
lib iomap: constify ioreadX() iomem argument (as in generic implementation) 2020-08-14 19:56:57 -07:00
mm Merge branch 'akpm' (patches from Andrew) 2020-08-15 08:02:03 -07:00
net 9p pull request for inclusion in 5.9 2020-08-15 08:34:36 -07:00
samples Kbuild updates for v5.9 2020-08-09 14:10:26 -07:00
scripts Kconfig updates for v5.9 2020-08-14 11:04:45 -07:00
security Merge branch 'akpm' (patches from Andrew) 2020-08-12 11:24:12 -07:00
sound sound fixes for 5.9-rc1 2020-08-14 15:58:57 -07:00
tools Cleanup, SECCOMP_FILTER support, message printing fixes, and other 2020-08-15 18:50:32 -07:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt Merge branch 'akpm' (patches from Andrew) 2020-08-12 11:24:12 -07:00
.clang-format block: add bio_for_each_bvec_all() 2020-05-25 11:25:24 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: Add ZSTD-compressed files 2020-07-31 11:50:49 +02:00
.mailmap mailmap: add entry for Greg Kurz 2020-08-14 19:56:56 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS CREDITS: Replace HTTP links with HTTPS ones 2020-07-23 14:53:58 -06:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS perf tools changes for v5.9: 2nd batch 2020-08-15 11:17:15 -07:00
Makefile Linux 5.9-rc1 2020-08-16 13:04:57 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.