linux-kernel - Re: [PATCH V4 1/5] perf: Add PERF_RECORD

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150721175454.GC16921@kernel.org>
Date:	Tue, 21 Jul 2015 14:54:54 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Adrian Hunter <adrian.hunter@...el.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Jiri Olsa <jolsa@...hat.com>,
	Stephane Eranian <eranian@...gle.com>,
	mathieu.poirier@...aro.org, Pawel Moll <pawel.moll@....com>
Subject: Re: [PATCH V4 1/5] perf: Add PERF_RECORD_SWITCH to indicate context
 switches

Em Tue, Jul 21, 2015 at 12:29:55PM +0200, Peter Zijlstra escreveu:
> On Tue, Jul 21, 2015 at 12:44:02PM +0300, Adrian Hunter wrote:
> > There are already two events for context switches, namely
> > the tracepoint sched:sched_switch and the software event
> > context_switches. Unfortunately neither are suitable for
> > use by non-privileged users for the purpose of synchronizing
> > hardware trace data (e.g. Intel PT) to the context switch.
> > 
> > Tracepoints are no good at all for non-privileged users
> > because they need either CAP_SYS_ADMIN or
> > /proc/sys/kernel/perf_event_paranoid <= -1.
> > 
> > On the other hand, kernel software events need either
> > CAP_SYS_ADMIN or /proc/sys/kernel/perf_event_paranoid <= 1.
> > 
> > Now many distributions do default perf_event_paranoid to 1
> > making context_switches a contender, except it has another
> > problem (which is also shared with sched:sched_switch)
> > which is that it happens before perf schedules events out
> > instead of after perf schedules events in. Whereas a
> > privileged user can see all the events anyway, a
> > non-privileged user only sees events for their own processes,
> > in other words they see when their process was scheduled out
> > not when it was scheduled in. That presents two problems to
> > use the event: 1. the information comes too late, so tools
> > have to look ahead in the event stream to find out what the
> > current state is 2. if they are unlucky tracing might have
> > stopped before the context-switches event is recorded.
> > 
> > This new PERF_RECORD_SWITCH event does not have those problems
> > and it also has a couple of other small advantages. It is
> > easier to use because it is an auxiliary event (like mmap,
> > comm and task events) which can be enabled by setting a single
> > bit. It is smaller than sched:sched_switch and easier to parse.
> > 
> > To make the event useful for privileged users also, if the
> > context is cpu-wide then the event record will be
> > PERF_RECORD_SWITCH_CPU_WIDE which is the same as
> > PERF_RECORD_SWITCH except it also provides the next or
> > previous pid/tid.
> > 
> > Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> 
> Acme, if you agree with the tools part, feel free to take the lot.

Looking at it, if all is well, I'll do it
 
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/