From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Will Deacon <will.deacon@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>, David Ahern <dsahern@gmail.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@gmail.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Question about barriers for ARM on tools/perf/
Date: Fri, 8 May 2015 11:04:59 -0300 [thread overview]
Message-ID: <20150508140459.GI7862@kernel.org> (raw)
Hi Will,
I am working on moving the stuff we have for mb/rmb/wmb from
tools/perf/perf-sys.h to tools/include/asm/barrier.h, redirecting
to tools/arch/$ARCH/include/asm/barrier.h, to make it look like the
kernel and who knows, at some point even share the source code.
For now I am getting just what is needed for work on having
atomic.h done in the same fashion, to implement refcounts for various
perf data structures, starting with struct thread, for which I have
a patch that makes perf survive in high core count machines where it
currently crashes, most nobably 'perf top'.
While doing that I noticed that arm64 implementation, lastly
fixed in:
f428ebd184c82a7914b2aa7e9f868918aaf7ea78
perf tools: Fix AAAAARGH64 memory barriers
By peterz, it implements those barriers as:
#define mb() asm volatile("dmb ish" ::: "memory")
#define wmb() asm volatile("dmb ishst" ::: "memory")
#define rmb() asm volatile("dmb ishld" ::: "memory")
Which are not the same as in the kernel, i.e. in
arch/arm64/include/asm/barrier.h, where the above are really smp_mb,
smp_wmb and smp_rmb.
Would it be enough for us to use the same implementation as the kernel?
I.e. make it be:
#define mb() asm volatile("dsb sy" ::: "memory")
#define wmb() asm volatile("dsb st" ::: "memory")
#define rmb() asm volatile("dsb ld" ::: "memory")
? If so I would then use those dsb/dmb macros, etc, to get tools/ to use
the proper instructions, etc.
I need now, for arm64, smp_mb, that is used by atomic_sub_return(), that
in turn is used by atomic_dec_and_test(), that I need for refcounts.
Can you clarify?
- Arnaldo
next reply other threads:[~2015-05-08 14:05 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-08 14:04 Arnaldo Carvalho de Melo [this message]
2015-05-08 14:16 ` Question about barriers for ARM on tools/perf/ Peter Zijlstra
2015-05-08 14:21 ` Will Deacon
2015-05-08 14:23 ` Peter Zijlstra
2015-05-08 14:21 ` Will Deacon
2015-05-08 14:25 ` Peter Zijlstra
2015-05-08 14:27 ` Will Deacon
2015-05-08 14:36 ` David Ahern
2015-05-08 14:37 ` Arnaldo Carvalho de Melo
2015-05-08 14:48 ` Will Deacon
2015-05-08 14:57 ` Arnaldo Carvalho de Melo
2015-05-08 15:27 ` Peter Zijlstra
2015-05-08 16:45 ` Will Deacon
2015-05-08 18:18 ` Arnaldo Carvalho de Melo
2015-05-08 14:52 ` Arnaldo Carvalho de Melo
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=20150508140459.GI7862@kernel.org \
--to=acme@kernel.org \
--cc=dsahern@gmail.com \
--cc=jolsa@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=namhyung@gmail.com \
--cc=peterz@infradead.org \
--cc=will.deacon@arm.com \
/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).