From: Peter Zijlstra <peterz@infradead.org>
To: Leo Yan <leo.yan@linaro.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>,
Adrian Hunter <adrian.hunter@intel.com>,
Ingo Molnar <mingo@redhat.com>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Namhyung Kim <namhyung@kernel.org>,
Andi Kleen <ak@linux.intel.com>,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 2/2] perf auxtrace: Optimize barriers with load-acquire and store-release
Date: Mon, 31 May 2021 17:55:25 +0200 [thread overview]
Message-ID: <YLUG7f3D4deX0/BF@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210531151049.GE9324@leoy-ThinkPad-X240s>
On Mon, May 31, 2021 at 11:10:49PM +0800, Leo Yan wrote:
> Hi Peter, Adrian,
>
> On Wed, May 19, 2021 at 10:03:19PM +0800, Leo Yan wrote:
> > Load-acquire and store-release are one-way permeable barriers, which can
> > be used to guarantee the memory ordering between accessing the buffer
> > data and the buffer's head / tail.
> >
> > This patch optimizes the memory ordering with the load-acquire and
> > store-release barriers.
>
> Is this patch okay for you?
Not without actual numbers; that's some terrible ifdef soup.
> Besides this patch, I have an extra question. You could see for
> accessing the AUX buffer's head and tail, it also support to use
> compiler build-in functions for atomicity accessing:
>
> __sync_val_compare_and_swap()
> __sync_bool_compare_and_swap()
>
> Since now we have READ_ONCE()/WRITE_ONCE(), do you think we still need
> to support __sync_xxx_compare_and_swap() atomicity?
>
> I checked the code for updating head and tail for the perf ring buffer
> (see ring_buffer_read_head() and ring_buffer_write_tail() in the file
> tools/include/linux/ring_buffer.h), which doesn't support
> __sync_xxx_compare_and_swap() anymore. This is why I wander if should
> drop __sync_xxx_compare_and_swap() atomicity for AUX ring buffer as
> well.
I'm not sure wth that code is even trying to do, that's some seriously
dodgy code.
next prev parent reply other threads:[~2021-05-31 17:24 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-19 14:03 [PATCH v1 1/2] perf auxtrace: Change to use SMP memory barriers Leo Yan
2021-05-19 14:03 ` [PATCH v1 2/2] perf auxtrace: Optimize barriers with load-acquire and store-release Leo Yan
2021-05-31 15:10 ` Leo Yan
2021-05-31 15:55 ` Peter Zijlstra [this message]
2021-05-31 19:03 ` Adrian Hunter
2021-06-01 6:33 ` Leo Yan
2021-06-01 6:58 ` Peter Zijlstra
2021-06-01 9:07 ` Adrian Hunter
2021-06-01 9:17 ` Peter Zijlstra
2021-06-01 9:45 ` Adrian Hunter
2021-06-01 9:48 ` Peter Zijlstra
2021-06-01 14:56 ` Leo Yan
2021-06-01 6:48 ` Peter Zijlstra
2021-05-27 7:54 ` [PATCH v1 1/2] perf auxtrace: Change to use SMP memory barriers Adrian Hunter
2021-05-27 8:11 ` Peter Zijlstra
2021-05-27 8:25 ` Adrian Hunter
2021-05-27 9:24 ` Adrian Hunter
2021-05-27 9:57 ` Peter Zijlstra
2021-05-31 14:53 ` Leo Yan
2021-05-31 15:48 ` Peter Zijlstra
2021-06-01 3:21 ` Leo Yan
2021-05-27 9:45 ` Peter Zijlstra
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