From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Ian Rogers <irogers@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Andi Kleen <ak@linux.intel.com>,
linux-kernel@vger.kernel.org,
Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH] perf bench: Add benchmark of find_next_bit
Date: Wed, 29 Jul 2020 17:44:09 -0300 [thread overview]
Message-ID: <20200729204409.GF433799@kernel.org> (raw)
In-Reply-To: <20200729195918.GE433799@kernel.org>
Em Wed, Jul 29, 2020 at 04:59:18PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Tue, Jul 28, 2020 at 08:51:52AM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Fri, Jul 24, 2020 at 12:19:59AM -0700, Ian Rogers escreveu:
> > > for_each_set_bit, or similar functions like for_each_cpu, may be hot
> > > within the kernel. If many bits were set then one could imagine on
> > > Intel a "bt" instruction with every bit may be faster than the function
> > > call and word length find_next_bit logic. Add a benchmark to measure
> > > this.
> >
> > Thanks, applied.
> > > This benchmark on AMD rome and Intel skylakex shows "bt" is not a good
> > > option except for very small bitmaps.
>
> > > +++ b/tools/perf/bench/find-bit-bench.c
>
> > > +#if defined(__i386__) || defined(__x86_64__)
> > > +static bool asm_test_bit(long nr, const unsigned long *addr)
> > > +{
> > > + bool oldbit;
> > > +
> > > + asm volatile("bt %2,%1"
> > > + : "=@ccc" (oldbit)
> > > + : "m" (*(unsigned long *)addr), "Ir" (nr) : "memory");
> > > +
> > > + return oldbit;
>
> Some old clang versions are not liking this:
Failed with:
clang version 3.8.0 (tags/RELEASE_380/final)
clang version 3.8.1 (tags/RELEASE_381/final)
clang version 4.0.0 (tags/RELEASE_400/final)
Alpine clang version 8.0.0 (tags/RELEASE_800/final) (based on LLVM 8.0.0)
Alpine clang version 5.0.0 (tags/RELEASE_500/final) (based on LLVM 5.0.0)
Alpine clang version 5.0.1 (tags/RELEASE_501/final) (based on LLVM 5.0.1)
Alpine clang version 5.0.1 (tags/RELEASE_502/final) (based on LLVM 5.0.1)
Worked with:
Alpine clang version 9.0.0 (https://git.alpinelinux.org/aports f7f0d2c2b8bcd6a5843401a9a702029556492689) (based on LLVM 9.0.0)
Alpine clang version 10.0.0 (https://gitlab.alpinelinux.org/alpine/aports.git 7445adce501f8473efdb93b17b5eaf2f1445ed4c)
Alpine clang version 10.0.0 (git://git.alpinelinux.org/aports 7445adce501f8473efdb93b17b5eaf2f1445ed4c)
Also failed for;
# grep FAIL dm.log/summary | grep -v alpine
alt:p8: FAIL
clang version 3.8.0 (tags/RELEASE_380/final)
alt:p9: FAIL
clang version 7.0.1
amazonlinux:1: FAIL
clang version 3.6.2 (tags/RELEASE_362/final)
amazonlinux:2: FAIL
clang version 7.0.1 (Amazon Linux 2 7.0.1-1.amzn2.0.2)
#
next prev parent reply other threads:[~2020-07-29 20:44 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-24 7:19 [PATCH] perf bench: Add benchmark of find_next_bit Ian Rogers
2020-07-24 14:45 ` Andi Kleen
2020-07-24 18:13 ` Ian Rogers
2020-07-28 11:51 ` Arnaldo Carvalho de Melo
2020-07-29 19:59 ` Arnaldo Carvalho de Melo
2020-07-29 20:44 ` Arnaldo Carvalho de Melo [this message]
2020-07-29 22:03 ` Ian Rogers
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200729204409.GF433799@kernel.org \
--to=acme@kernel.org \
--cc=ak@linux.intel.com \
--cc=alexander.shishkin@linux.intel.com \
--cc=eranian@google.com \
--cc=irogers@google.com \
--cc=jolsa@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=mingo@redhat.com \
--cc=namhyung@kernel.org \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).