From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753629Ab2JOQes (ORCPT ); Mon, 15 Oct 2012 12:34:48 -0400 Received: from mail-bk0-f46.google.com ([209.85.214.46]:42257 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753106Ab2JOQeq (ORCPT ); Mon, 15 Oct 2012 12:34:46 -0400 Subject: Re: [RFC PATCH] posix timers: allocate timer id per task From: Eric Dumazet To: Stanislav Kinsbursky Cc: peterz@infradead.org, mingo@redhat.com, tglx@linutronix.de, linux-kernel@vger.kernel.org, devel@openvz.org In-Reply-To: <20121015161559.7806.72762.stgit@localhost.localdomain> References: <20121015161559.7806.72762.stgit@localhost.localdomain> Content-Type: text/plain; charset="UTF-8" Date: Mon, 15 Oct 2012 18:34:43 +0200 Message-ID: <1350318883.3954.321.camel@edumazet-glaptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2012-10-15 at 20:17 +0400, Stanislav Kinsbursky wrote: > This patch is required CRIU project (www.criu.org). > To migrate processes with posix timers we have to make sure, that we can > restore posix timer with proper id. > Currently, this is not true, because timer ids are allocated globally. > So, this is precursor patch and it's purpose is make posix timer id to be > allocated per task. > > Patch replaces global idr with global hash table for posix timers and > makes timer ids unique not globally, but per task. Next free timer id is type > of integer and stored on signal struct (posix_timer_id). If free timer id > reaches negative value on timer creation, it will be dropped to zero and > -EAGAIN will be returned to user. > Hash table is size of page (4KB). > Key is constructed as follows: > key = hash_ptr(current->signal) ^ hash_32(posix_timer_id); > > Signed-off-by: Stanislav Kinsbursky Hmm, it seems you removed idr, rcu friendly, and reinstated a fixed size hash table, protected by a _single_ spinlock ? Oh well. Please take a look at commit 8af088710d1e, and make sure you fix your problem and keep performance as good as before.