From: Peter Zijlstra <peterz@infradead.org>
To: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, adrian.hunter@intel.com,
x86@kernel.org, hpa@zytor.com, acme@infradead.org
Subject: Re: [PATCH 2/3] perf/x86/intel/pt: Add an option to not force PSB+ on every schedule-in
Date: Thu, 30 Jul 2015 12:43:10 +0200 [thread overview]
Message-ID: <20150730104310.GW19282@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1437140050-23363-3-git-send-email-alexander.shishkin@linux.intel.com>
On Fri, Jul 17, 2015 at 04:34:09PM +0300, Alexander Shishkin wrote:
> Currently, the PT driver zeroes out the status register every time before
> starting the event. However, all the writable bits are already taken care
> of in pt_handle_status() function, except the new PacketByteCnt field,
> which in new versions of PT contains the number of packet bytes written
> since the last sync (PSB) packet. Zeroing it out before enabling PT forces
> a sync packet to be written. This means that, with the existing code, a
> sync packet (PSB and PSBEND, 18 bytes in total) will be generated every
> time a PT event is scheduled in.
>
> To avoid these unnecessary syncs and save a WRMSR in the fast path, this
> patch adds a new attribute config bit "no_force_psb", which will disable
> this zeroing WRMSR.
Why is this exposed?
next prev parent reply other threads:[~2015-07-30 10:43 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-17 13:34 [PATCH 0/3] perf/x86/intel/pt: Add new packet enables Alexander Shishkin
2015-07-17 13:34 ` [PATCH 1/3] perf/x86/intel/pt: Add new timing " Alexander Shishkin
2015-07-30 10:40 ` Peter Zijlstra
2015-07-30 11:57 ` Alexander Shishkin
2015-07-30 12:14 ` Peter Zijlstra
2015-07-30 13:15 ` [PATCH v1] " Alexander Shishkin
2015-08-04 8:55 ` [tip:perf/core] " tip-bot for Alexander Shishkin
2015-07-17 13:34 ` [PATCH 2/3] perf/x86/intel/pt: Add an option to not force PSB+ on every schedule-in Alexander Shishkin
2015-07-30 10:43 ` Peter Zijlstra [this message]
2015-07-30 11:53 ` Alexander Shishkin
2015-07-30 12:13 ` Peter Zijlstra
2015-07-30 12:49 ` Alexander Shishkin
2015-07-30 13:36 ` Alexander Shishkin
2015-07-30 13:48 ` [PATCH v1] perf/x86/intel/pt: Do not force sync packets " Alexander Shishkin
2015-07-30 15:24 ` Alexander Shishkin
2015-08-04 8:55 ` [tip:perf/core] " tip-bot for Alexander Shishkin
2015-07-31 11:47 ` [PATCH v2] " Alexander Shishkin
2015-07-17 13:34 ` [PATCH 3/3] perf/x86/intel/bts: Set itrace_started in pmu::start to match the new logic Alexander Shishkin
2015-09-08 12:02 ` Alexander Shishkin
2015-09-08 12:28 ` Peter Zijlstra
2015-09-13 10:56 ` [tip:perf/core] perf/x86/intel/bts: Set event-> hw.itrace_started " tip-bot for Alexander Shishkin
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