From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757903AbbEVPcx (ORCPT ); Fri, 22 May 2015 11:32:53 -0400 Received: from mga11.intel.com ([192.55.52.93]:36421 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757207AbbEVPb2 (ORCPT ); Fri, 22 May 2015 11:31:28 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.13,476,1427785200"; d="scan'208";a="497091491" From: Alexander Shishkin To: Peter Zijlstra , Ingo Molnar Cc: linux-kernel@vger.kernel.org, Paul Mackerras , adrian.hunter@intel.com, x86@kernel.org, hpa@zytor.com, acme@infradead.org, Alexander Shishkin Subject: [PATCH v1 4/7] perf/x86/intel/pt: Document pt_buffer_reset_markers() Date: Fri, 22 May 2015 18:30:23 +0300 Message-Id: <1432308626-18845-5-git-send-email-alexander.shishkin@linux.intel.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1432308626-18845-1-git-send-email-alexander.shishkin@linux.intel.com> References: <1432308626-18845-1-git-send-email-alexander.shishkin@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The comments in the driver don't make it absolutely clear as to what exactly is the calling order and other possible constraints of buffer management functions. Document constraints and calling order for the buffer configuration functions. While at it, replace a redundant check in pt_buffer_reset_markers() with an explanation why it is not needed. Signed-off-by: Alexander Shishkin --- arch/x86/kernel/cpu/perf_event_intel_pt.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/cpu/perf_event_intel_pt.c b/arch/x86/kernel/cpu/perf_event_intel_pt.c index 8a4595650d..b2746eafa0 100644 --- a/arch/x86/kernel/cpu/perf_event_intel_pt.c +++ b/arch/x86/kernel/cpu/perf_event_intel_pt.c @@ -609,7 +609,12 @@ static unsigned int pt_topa_next_entry(struct pt_buffer *buf, unsigned int pg) * @handle: Current output handle. * * Place INT and STOP marks to prevent overwriting old data that the consumer - * hasn't yet collected. + * hasn't yet collected and waking up the consumer after a certain fraction of + * the buffer has filled up. Only needed and sensible for non-snapshot counters. + * + * This obviously relies on buf::head to figure out buffer markers, so it has + * to be called after pt_buffer_reset_offsets() and before the hardware tracing + * is enabled. */ static int pt_buffer_reset_markers(struct pt_buffer *buf, struct perf_output_handle *handle) @@ -618,9 +623,6 @@ static int pt_buffer_reset_markers(struct pt_buffer *buf, unsigned long head = local64_read(&buf->head); unsigned long idx, npages, wakeup; - if (buf->snapshot) - return 0; - /* can't stop in the middle of an output region */ if (buf->output_off + handle->size + 1 < sizes(TOPA_ENTRY(buf->cur, buf->cur_idx)->size)) @@ -901,6 +903,7 @@ void intel_pt_interrupt(void) } pt_buffer_reset_offsets(buf, pt->handle.head); + /* snapshot counters don't use PMI, so it's safe */ ret = pt_buffer_reset_markers(buf, &pt->handle); if (ret) { perf_aux_output_end(&pt->handle, 0, true); -- 2.1.4