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>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Mathieu Poirier <mathieu.poirier@linaro.org>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Mike Leach <mike.leach@linaro.org>,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v4 03/11] coresight: tmc-etf: Add comment for store ordering
Date: Tue, 13 Jul 2021 14:56:06 +0200 [thread overview]
Message-ID: <20210713125606.GB4170@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20210711104105.505728-4-leo.yan@linaro.org>
On Sun, Jul 11, 2021 at 06:40:57PM +0800, Leo Yan wrote:
> AUX ring buffer is required to separate the data store and aux_head
> store, since the function CS_LOCK() has contained memory barrier mb(),
> mb() is a more conservative barrier than smp_wmb() on Arm32/Arm64, thus
> it's needless to add any explicit barrier anymore.
>
> Add comment to make clear for the barrier usage for ETF.
>
> Signed-off-by: Leo Yan <leo.yan@linaro.org>
> ---
> drivers/hwtracing/coresight/coresight-tmc-etf.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> index 45b85edfc690..9a42ee689921 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> @@ -553,6 +553,12 @@ static unsigned long tmc_update_etf_buffer(struct coresight_device *csdev,
> if (buf->snapshot)
> handle->head += to_read;
>
> + /*
> + * AUX ring buffer requires to use memory barrier to separate the trace
> + * data store and aux_head store, because CS_LOCK() contains mb() which
> + * gives more heavy barrier than smp_wmb(), it's not necessary to
> + * explicitly invoke any barrier.
> + */
> CS_LOCK(drvdata->base);
'more heavy' is not a correctness argument :-)
The argument to make here is that CS_LOCK() ensures completion /
visibility of the hardware buffer.
next prev parent reply other threads:[~2021-07-13 12:57 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-11 10:40 [PATCH v4 00/11] perf: Refine barriers for AUX ring buffer Leo Yan
2021-07-11 10:40 ` [PATCH v4 01/11] perf/ring_buffer: Add comment for barriers on " Leo Yan
2021-07-11 10:40 ` [PATCH v4 02/11] coresight: tmc-etr: Add barrier after updating " Leo Yan
2021-07-12 10:40 ` Suzuki K Poulose
2021-07-12 10:54 ` Leo Yan
2021-07-11 10:40 ` [PATCH v4 03/11] coresight: tmc-etf: Add comment for store ordering Leo Yan
2021-07-13 12:56 ` Peter Zijlstra [this message]
2021-07-13 15:49 ` Leo Yan
2021-07-11 10:40 ` [PATCH v4 04/11] perf/x86: Add barrier after updating bts Leo Yan
2021-07-13 13:01 ` Peter Zijlstra
2021-07-11 10:40 ` [PATCH v4 05/11] perf auxtrace: Use WRITE_ONCE() for updating aux_tail Leo Yan
2021-07-11 10:41 ` [PATCH v4 06/11] perf auxtrace: Drop legacy __sync functions Leo Yan
2021-07-11 10:41 ` [PATCH v4 07/11] perf auxtrace: Remove auxtrace_mmap__read_snapshot_head() Leo Yan
2021-07-12 14:32 ` Adrian Hunter
2021-07-13 13:10 ` Leo Yan
2021-07-11 10:41 ` [PATCH v4 08/11] perf: Cleanup for HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT Leo Yan
2021-07-11 10:41 ` [PATCH v4 09/11] tools: Remove feature-sync-compare-and-swap feature detection Leo Yan
2021-07-11 10:41 ` [PATCH v4 10/11] perf env: Set flag for kernel is 64-bit mode Leo Yan
2021-07-12 14:37 ` Adrian Hunter
2021-07-12 18:14 ` Arnaldo Carvalho de Melo
2021-07-13 15:09 ` Leo Yan
2021-07-13 17:31 ` Hunter, Adrian
2021-07-14 13:59 ` Arnaldo Carvalho de Melo
2021-07-14 14:00 ` Arnaldo Carvalho de Melo
2021-07-23 7:11 ` Leo Yan
2021-07-11 10:41 ` [PATCH v4 11/11] perf auxtrace: Add compat_auxtrace_mmap__{read_head|write_tail} Leo Yan
2021-07-12 14:44 ` Russell King (Oracle)
2021-07-13 15:46 ` Leo Yan
2021-07-13 16:14 ` Russell King (Oracle)
2021-07-13 18:13 ` Catalin Marinas
2021-07-14 8:40 ` Russell King (Oracle)
2021-07-23 7:23 ` Leo Yan
2021-07-13 7:07 ` Adrian Hunter
2021-07-13 15:48 ` Leo Yan
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=20210713125606.GB4170@worktop.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=acme@kernel.org \
--cc=adrian.hunter@intel.com \
--cc=alexander.shishkin@linux.intel.com \
--cc=bp@alien8.de \
--cc=coresight@lists.linaro.org \
--cc=hpa@zytor.com \
--cc=jolsa@redhat.com \
--cc=leo.yan@linaro.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-perf-users@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=mathieu.poirier@linaro.org \
--cc=mike.leach@linaro.org \
--cc=mingo@redhat.com \
--cc=namhyung@kernel.org \
--cc=suzuki.poulose@arm.com \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/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).