[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAOp6jLY9yFZC_3x_fi2m9tinDwQ-Ag_3F-P0EOc4oGpVr4oujQ@mail.gmail.com>
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
Powered by blists - more mailing lists