linux-kernel - Re: (subset) [PATCH v6 00/17] coresight: Use per-sink trace ID maps for Perf sessions

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Message-Id: <172433479466.350842.6920589600831615538.b4-ty@arm.com>
Date: Thu, 22 Aug 2024 15:05:53 +0100
From: Suzuki K Poulose <suzuki.poulose@....com>
To: anshuman.khandual@....com,
	James Clark <james.clark@...aro.org>,
	gankulkarni@...amperecomputing.com,
	mike.leach@...aro.org,
	leo.yan@...ux.dev,
	coresight@...ts.linaro.org
Cc: Suzuki K Poulose <suzuki.poulose@....com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	John Garry <john.g.garry@...cle.com>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ian Rogers <irogers@...gle.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Mark Rutland <mark.rutland@....com>,
	linux-perf-users@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	linux-stm32@...md-mailman.stormreply.com,
	"Liang, Kan" <kan.liang@...ux.intel.com>,
	Will Deacon <will@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	linux-kernel@...r.kernel.org,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	linux-arm-kernel@...ts.infradead.org,
	Adrian Hunter <adrian.hunter@...el.com>,
	Jiri Olsa <jolsa@...nel.org>,
	James Clark <james.clark@....com>
Subject: Re: (subset) [PATCH v6 00/17] coresight: Use per-sink trace ID maps for Perf sessions

On Mon, 22 Jul 2024 11:11:42 +0100, James Clark wrote:
> This will allow sessions with more than CORESIGHT_TRACE_IDS_MAX ETMs
> as long as there are fewer than that many ETMs connected to each sink.
> 
> Each sink owns its own trace ID map, and any Perf session connecting to
> that sink will allocate from it, even if the sink is currently in use by
> other users. This is similar to the existing behavior where the dynamic
> trace IDs are constant as long as there is any concurrent Perf session
> active. It's not completely optimal because slightly more IDs will be
> used than necessary, but the optimal solution involves tracking the PIDs
> of each session and allocating ID maps based on the session owner. This
> is difficult to do with the combination of per-thread and per-cpu modes
> and some scheduling issues. The complexity of this isn't likely to worth
> it because even with multiple users they'd just see a difference in the
> ordering of ID allocations rather than hitting any limits (unless the
> hardware does have too many ETMs connected to one sink).
> 
> [...]

Applied, the kernel driver changes to coresight/next. Thanks!

[09/17] coresight: Remove unused ETM Perf stubs
        https://git.kernel.org/coresight/c/34172002bdac
[10/17] coresight: Clarify comments around the PID of the sink owner
        https://git.kernel.org/coresight/c/eda1d11979c0
[11/17] coresight: Move struct coresight_trace_id_map to common header
        https://git.kernel.org/coresight/c/acb0184fe9bc
[12/17] coresight: Expose map arguments in trace ID API
        https://git.kernel.org/coresight/c/7e52877868ae
[13/17] coresight: Make CPU id map a property of a trace ID map
        https://git.kernel.org/coresight/c/d53c8253c782
[14/17] coresight: Use per-sink trace ID maps for Perf sessions
        https://git.kernel.org/coresight/c/5ad628a76176
[15/17] coresight: Remove pending trace ID release mechanism
        https://git.kernel.org/coresight/c/de0029fdde86
[16/17] coresight: Emit sink ID in the HW_ID packets
        https://git.kernel.org/coresight/c/487eec8da80a
[17/17] coresight: Make trace ID map spinlock local to the map
        https://git.kernel.org/coresight/c/988d40a4d4e7

Best regards,
-- 
Suzuki K Poulose <suzuki.poulose@....com>