From: Ravi Bangoria <ravi.bangoria@amd.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: acme@kernel.org, alexander.shishkin@linux.intel.com,
jolsa@redhat.com, namhyung@kernel.org, songliubraving@fb.com,
eranian@google.com, ak@linux.intel.com, mark.rutland@arm.com,
frederic@kernel.org, maddy@linux.ibm.com, irogers@google.com,
will@kernel.org, robh@kernel.org, mingo@redhat.com,
catalin.marinas@arm.com, linux-arm-kernel@lists.infradead.org,
linux-perf-users@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
sandipan.das@amd.com, ananth.narayan@amd.com,
kim.phillips@amd.com, santosh.shukla@amd.com,
ravi.bangoria@amd.com
Subject: Re: [PATCH] perf: Rewrite core context handling
Date: Mon, 5 Sep 2022 10:10:14 +0530 [thread overview]
Message-ID: <8f5b618e-e0a1-c5f2-3d4d-a41ea96fd59c@amd.com> (raw)
In-Reply-To: <YxCXqjfiJca3izQd@hirez.programming.kicks-ass.net>
> So the basic issue I mentioned is that:
>
>
> /*
> * ,------------------------[1:n]---------------------.
> * V V
> * perf_event_context <-[1:n]-> perf_event_pmu_context <--- perf_event
> * ^ ^ | |
> * `--------[1:n]---------' `-[n:1]-> pmu <-[1:n]-'
> *
> *
> * XXX destroy epc when empty
> * refcount, !rcu
> *
> * XXX epc locking
> *
> * event->pmu_ctx ctx->mutex && inactive
> * ctx->pmu_ctx_list ctx->mutex && ctx->lock
> *
> */
> struct perf_event_pmu_context {
> ...
> atomic_t refcount; /* event <-> epc */
> ...
> }
>
> But that then also suggests that:
>
> struct perf_event_context {
> ...
> refcount_t refcount;
> ...
> }
>
> should be: ctx <-> epc, and that is not so, the ctx::refcount still
> counts the number of events.
>
> Now this might not be bad, but it is confusing.
I don't have strong opinion, but we store events in ctx, not in pmu_ctx.
So, I think it makes sense to keep refcount as ctx <-> event?
[...]
> +void perf_pmu_migrate_context(struct pmu *pmu, int src_cpu, int dst_cpu)
> +{
> + struct perf_event_context *src_ctx, *dst_ctx;
> + LIST_HEAD(events);
> +
> + src_ctx = &per_cpu_ptr(&cpu_context, src_cpu)->ctx;
> + dst_ctx = &per_cpu_ptr(&cpu_context, dst_cpu)->ctx;
> +
> + /*
> + * See perf_event_ctx_lock() for comments on the details
> + * of swizzling perf_event::ctx.
> + */
> + mutex_lock_double(&src_ctx->mutex, &dst_ctx->mutex);
> +
> + __perf_pmu_remove(src_ctx, src_cpu, pmu, &src_src->pinned_groups, &events);
> + __perf_pmu_remove(src_ctx, src_cpu, pmu, &src_src->flexible_groups, &events);
Rbtrees does not contain sibling events. Shouldn't we continue using
event_list here?
Thanks,
Ravi
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next prev parent reply other threads:[~2022-09-05 4:43 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20220829113347.295-1-ravi.bangoria@amd.com>
2022-08-29 12:04 ` [PATCH] perf: Rewrite core context handling Peter Zijlstra
2022-08-29 14:40 ` Peter Zijlstra
2022-09-01 10:35 ` Ravi Bangoria
2022-09-01 11:29 ` Peter Zijlstra
2022-09-05 4:40 ` Ravi Bangoria [this message]
2022-09-06 5:50 ` Ravi Bangoria
2022-10-10 10:23 ` Peter Zijlstra
2022-10-10 11:01 ` Ravi Bangoria
2022-09-07 11:28 ` Ravi Bangoria
2022-10-10 10:14 ` Peter Zijlstra
2022-10-10 10:59 ` Ravi Bangoria
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