Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754396Ab3GOIMw (ORCPT ); Mon, 15 Jul 2013 04:12:52 -0400 Received: from mga14.intel.com ([143.182.124.37]:13628 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754366Ab3GOIMa (ORCPT ); Mon, 15 Jul 2013 04:12:30 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.89,667,1367996400"; d="scan'208";a="331446081" From: "Kirill A. Shutemov" To: Andi Kleen Cc: acme@infradead.org, linux-kernel@vger.kernel.org, Andi Kleen , h.mitake@gmail.com, kirill.shutemov@linux.jf.intel.com In-Reply-To: <1373675551-18684-1-git-send-email-andi@firstfloor.org> References: <1373675551-18684-1-git-send-email-andi@firstfloor.org> Subject: RE: [PATCH] perf, tools, bench: Fix memcpy benchmark for large sizes Content-Transfer-Encoding: 7bit Message-Id: <20130715081532.52D85E0090@blue.fi.intel.com> Date: Mon, 15 Jul 2013 11:15:32 +0300 (EEST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1539 Lines: 45 Andi Kleen wrote: > From: Andi Kleen > > glibc calloc() has an optimization to not explicitely memset() > very large calloc allocations that just came from mmap(), > because they are known to be zero. > > This could result in the perf memcpy benchmark reading only from > the zero page, which gives unrealistic results. > > Always call memset explicitly on the source area to avoid this problem. > > Cc: h.mitake@gmail.com > Cc: kirill.shutemov@linux.intel.com > Signed-off-by: Andi Kleen Acked-by: Kirill A. Shutemov > --- > tools/perf/bench/mem-memcpy.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/tools/perf/bench/mem-memcpy.c b/tools/perf/bench/mem-memcpy.c > index 93c83e3..690f75f 100644 > --- a/tools/perf/bench/mem-memcpy.c > +++ b/tools/perf/bench/mem-memcpy.c > @@ -117,6 +117,8 @@ static void alloc_mem(void **dst, void **src, size_t length) > *src = zalloc(length); > if (!src) > die("memory allocation failed - maybe length is too large?\n"); > + /* Make sure to always replace the zero pages even if MMAP_THRESH is crossed */ > + memset(src, 0, length); > } > > static u64 do_memcpy_cycle(memcpy_t fn, size_t len, bool prefault) > -- > 1.8.1.4 -- Kirill A. Shutemov -- 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/