Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752626Ab0GOGuA (ORCPT ); Thu, 15 Jul 2010 02:50:00 -0400 Received: from mga01.intel.com ([192.55.52.88]:31545 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751663Ab0GOGt6 (ORCPT ); Thu, 15 Jul 2010 02:49:58 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.55,206,1278313200"; d="scan'208";a="818325321" Subject: [PATCH] Don't apply for write lock on tasklist_lock if parent doesn't ptrace other processes From: "Zhang, Yanmin" To: LKML Cc: Andrew Morton , andi.kleen@intel.com Content-Type: text/plain; charset="ISO-8859-1" Date: Thu, 15 Jul 2010 14:51:03 +0800 Message-Id: <1279176663.2096.1264.camel@ymzhang.sh.intel.com> Mime-Version: 1.0 X-Mailer: Evolution 2.28.0 (2.28.0-2.fc12) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1240 Lines: 32 We run some sub-cases (fork, exec, pipe, tcp, udp) of aim7 on 8-socket machine. Perf shows write_lock_irq(&tasklist_lock) consumes more than 50% cpu time. One hot caller is exit_ptrace. If the exiting process doesn't ptrace other processes, kernel needn't apply for the write lock on tasklist_lock. With below patch against kernel 2.6.35-rc5, we get more than 10% result improvement. Signed-off-by: Zhang Yanmin --- diff -Nraup linux-2.6.35-rc5/kernel/ptrace.c linux-2.6.35-rc5_ptrace/kernel/ptrace.c --- linux-2.6.35-rc5/kernel/ptrace.c 2010-07-16 14:01:15.000000000 +0800 +++ linux-2.6.35-rc5_ptrace/kernel/ptrace.c 2010-07-16 14:03:20.000000000 +0800 @@ -331,6 +331,9 @@ void exit_ptrace(struct task_struct *tra struct task_struct *p, *n; LIST_HEAD(ptrace_dead); + if (list_empty(&tracer->ptraced)) + return; + write_lock_irq(&tasklist_lock); list_for_each_entry_safe(p, n, &tracer->ptraced, ptrace_entry) { if (__ptrace_detach(tracer, p)) -- 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/