From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753069Ab2JSH4t (ORCPT ); Fri, 19 Oct 2012 03:56:49 -0400 Received: from mail-bk0-f46.google.com ([209.85.214.46]:39902 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751816Ab2JSH4s (ORCPT ); Fri, 19 Oct 2012 03:56:48 -0400 Subject: Re: [PATCH v4] posix timers: allocate timer id per process From: Eric Dumazet To: Stanislav Kinsbursky Cc: peterz@infradead.org, mingo@redhat.com, tglx@linutronix.de, devel@openvz.org, linux-kernel@vger.kernel.org, xemul@parallels.com In-Reply-To: <20121019074912.10745.339.stgit@localhost.localdomain> References: <20121019074912.10745.339.stgit@localhost.localdomain> Content-Type: text/plain; charset="UTF-8" Date: Fri, 19 Oct 2012 09:56:40 +0200 Message-ID: <1350633401.2293.245.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 Fri, 2012-10-19 at 11:50 +0400, Stanislav Kinsbursky wrote: > v4: > 1) a couple of coding style fixes (lines over 80 characters) > > v3: > 1) hash calculation simlified to improve perfomance. > > v2: > 1) Hash table become RCU-friendly. Hash table search now done under RCU lock > protection. This should not be in the changelog, only after the --- separator. > I've tested scalability on KVM with 4 CPU. The testing environment was build > of 10 processes, each had 512 posix timers running (SIGSEV_NONE) and was > calling timer_gettime() in loop. With all this stuff being running, I was > measuring time of calling of syscall timer_gettime() 10000 times. > > Without this patch: ~7ms > With this patch : ~7ms > > 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 process. > > 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. I wonder if some applications relied on our idr, assuming they would get low values for their timer id. (We could imagine some applications use a table indexed by the timer id) > Hash table is size of page (4KB). Only on x86_64. Why not instead saying hashtable has 512 slots ? > Key is constructed as follows: > key = hash_32(current->signal) ^ hash_32(posix_timer_id); This is outdated. > > Signed-off-by: Stanislav Kinsbursky > --- Thanks