Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1195906

Re: [PATCH 2/3] perf/x86/intel/pt: Add an option to not force PSB+ on every schedule-in

Show all headers | View raw

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?

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next | Find similar | Unroll thread

Thread

Re: [PATCH 2/3] perf/x86/intel/pt: Add an option to not force PSB+  on every schedule-in Peter Zijlstra <peterz@infradead.org> - 2015-07-30 12:50 +0200

csiph-web