From: Josh Poimboeuf <jpoimboe@kernel.org>
To: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@kernel.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
linux-kernel@vger.kernel.org, x86@kernel.org,
Indu Bhagat <indu.bhagat@oracle.com>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@kernel.org>, Ian Rogers <irogers@google.com>,
Adrian Hunter <adrian.hunter@intel.com>,
linux-perf-users@vger.kernel.org, Mark Brown <broonie@kernel.org>,
linux-toolchains@vger.kernel.org
Subject: Re: [PATCH RFC 04/10] perf: Introduce deferred user callchains
Date: Sat, 11 Nov 2023 10:54:30 -0800 [thread overview]
Message-ID: <20231111185430.7j5izoshctdmu5h5@treble> (raw)
In-Reply-To: <20231111184908.ym4l6cwzwnkl7e6m@treble>
On Sat, Nov 11, 2023 at 10:49:10AM -0800, Josh Poimboeuf wrote:
> On Fri, Nov 10, 2023 at 10:57:58PM -0800, Namhyung Kim wrote:
> > > +static void perf_pending_task_unwind(struct perf_event *event)
> > > +{
> > > + struct pt_regs *regs = task_pt_regs(current);
> > > + struct perf_output_handle handle;
> > > + struct perf_event_header header;
> > > + struct perf_sample_data data;
> > > + struct perf_callchain_entry *callchain;
> > > +
> > > + callchain = kmalloc(sizeof(struct perf_callchain_entry) +
> > > + (sizeof(__u64) * event->attr.sample_max_stack) +
> > > + (sizeof(__u64) * 1) /* one context */,
> > > + GFP_KERNEL);
> >
> > Any chance it can reuse get_perf_callchain() instead of
> > allocating the callchains every time?
>
> I don't think so, because if it gets preempted, the new task might also
> need to do an unwind. But there's only one task-context callchain per
> CPU.
BTW it's not just preemption, this code can also block when the unwinder
tries to copy from user space. So disabling preemption isn't an option.
--
Josh
next prev parent reply other threads:[~2023-11-11 18:54 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-09 0:41 [PATCH RFC 00/10] perf: user space sframe unwinding Josh Poimboeuf
2023-11-09 0:41 ` [PATCH RFC 01/10] perf: Remove get_perf_callchain() 'init_nr' argument Josh Poimboeuf
2023-11-11 6:09 ` Namhyung Kim
2023-11-09 0:41 ` [PATCH RFC 02/10] perf: Remove get_perf_callchain() 'crosstask' argument Josh Poimboeuf
2023-11-11 6:11 ` Namhyung Kim
2023-11-11 20:53 ` Jordan Rome
2023-11-09 0:41 ` [PATCH RFC 03/10] perf: Simplify get_perf_callchain() user logic Josh Poimboeuf
2023-11-11 6:11 ` Namhyung Kim
2023-11-09 0:41 ` [PATCH RFC 04/10] perf: Introduce deferred user callchains Josh Poimboeuf
2023-11-11 6:57 ` Namhyung Kim
2023-11-11 18:49 ` Josh Poimboeuf
2023-11-11 18:54 ` Josh Poimboeuf [this message]
2023-11-13 16:56 ` Namhyung Kim
2023-11-13 17:21 ` Peter Zijlstra
2023-11-13 17:48 ` Namhyung Kim
2023-11-13 18:49 ` Peter Zijlstra
2023-11-13 19:16 ` Namhyung Kim
2023-11-15 16:13 ` Namhyung Kim
2023-11-20 14:03 ` Peter Zijlstra
2023-11-09 0:41 ` [PATCH RFC 05/10] perf/x86: Add HAVE_PERF_CALLCHAIN_DEFERRED Josh Poimboeuf
2023-11-09 0:41 ` [PATCH RFC 06/10] unwind: Introduce generic user space unwinding interfaces Josh Poimboeuf
2023-11-09 0:41 ` [PATCH RFC 07/10] unwind/x86: Add HAVE_USER_UNWIND Josh Poimboeuf
2023-11-09 0:41 ` [PATCH RFC 08/10] perf/x86: Use user_unwind interface Josh Poimboeuf
2023-11-09 0:41 ` [PATCH RFC 09/10] unwind: Introduce SFrame user space unwinding Josh Poimboeuf
2023-11-09 19:31 ` Indu Bhagat
2023-11-09 19:37 ` Josh Poimboeuf
2023-11-09 19:49 ` Steven Rostedt
2023-11-09 19:53 ` Josh Poimboeuf
2023-11-09 0:41 ` [PATCH RFC 10/10] unwind/x86/64: Add HAVE_USER_UNWIND_SFRAME Josh Poimboeuf
2023-11-09 0:45 ` [PATCH RFC 00/10] perf: user space sframe unwinding Josh Poimboeuf
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