linux-kernel - Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the kernel in the "skid" region

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 28 Jun 2017 10:48:33 -0700
From:   "Robert O'Callahan" <robert@...llahan.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Kyle Huey <me@...ehuey.com>, "Jin, Yao" <yao.jin@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        stable@...r.kernel.org,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vince Weaver <vincent.weaver@...ne.edu>, acme@...nel.org,
        jolsa@...nel.org, kan.liang@...el.com,
        Will Deacon <will.deacon@....com>, gregkh@...uxfoundation.org,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the
 kernel in the "skid" region

On Wed, Jun 28, 2017 at 10:19 AM, Mark Rutland <mark.rutland@....com> wrote:
> It seems odd that an event without any samples to take has a sample
> period. I'm surprised that there's not *some* sample_type set.

Yes, it is a bit odd :-). Rather than trying to gather some limited
set of information about the target process, we want to interrupt its
execution after a particular number of events have occurred.

The bigger picture here is that we're replaying a previously recorded
process execution. We want to the process to run until it reaches a
particular state that occurred during recording; that state is
identified by a value for the performance counter (retired conditional
branches) plus the values of the general-purpose registers. So our
first step is to run the process until the performance counter reaches
a value less than but "close to" the target value. (We know the
process will be interrupted after a number of extra events have
occurred, so we set the sample period to a value less than the target
by a heuristic "maximum skid size".)

Rob
-- 
lbir ye,ea yer.tnietoehr  rdn rdsme,anea lurpr  edna e hnysnenh hhe uresyf toD
selthor  stor  edna  siewaoeodm  or v sstvr  esBa  kbvted,t rdsme,aoreseoouoto
o l euetiuruewFa  kbn e hnystoivateweh uresyf tulsa rehr  rdm  or rnea lurpr
.a war hsrer holsa rodvted,t  nenh hneireseoouot.tniesiewaoeivatewt sstvr  esn