From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965104AbWJJSgg (ORCPT ); Tue, 10 Oct 2006 14:36:36 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965115AbWJJSgg (ORCPT ); Tue, 10 Oct 2006 14:36:36 -0400 Received: from mail.impinj.com ([206.169.229.170]:32387 "EHLO earth.impinj.com") by vger.kernel.org with ESMTP id S965104AbWJJSgf (ORCPT ); Tue, 10 Oct 2006 14:36:35 -0400 From: Vadim Lobanov To: Eric Dumazet Subject: Re: [PATCH 2/5] fdtable: Make fdarray and fdsets equal in size. Date: Tue, 10 Oct 2006 11:36:34 -0700 User-Agent: KMail/1.9.1 Cc: akpm@osdl.org, linux-kernel@vger.kernel.org References: <200610052151.04490.vlobanov@speakeasy.net> <200610101912.56280.dada1@cosmosbay.com> In-Reply-To: <200610101912.56280.dada1@cosmosbay.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200610101136.34341.vlobanov@speakeasy.net> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tuesday 10 October 2006 10:12, Eric Dumazet wrote: > On Friday 06 October 2006 06:51, Vadim Lobanov wrote: > > - nfds = max_t(int, 8 * L1_CACHE_BYTES, roundup_pow_of_two(nr + 1)); > > - if (nfds > NR_OPEN) > > - nfds = NR_OPEN; > > - > > - new_openset = alloc_fdset(nfds); > > - new_execset = alloc_fdset(nfds); > > - if (!new_openset || !new_execset) > > - goto out; > > - fdt->open_fds = new_openset; > > - fdt->close_on_exec = new_execset; > > - fdt->max_fdset = nfds; > > - > > nfds = NR_OPEN_DEFAULT; > > /* > > * Expand to the max in easy steps, and keep expanding it until > > @@ -271,15 +254,21 @@ static struct fdtable *alloc_fdtable(int > > nfds = NR_OPEN; > > } > > } while (nfds <= nr); > > If I understand well, we may allocate very small fdset, while previous > minimum size was L1_CACHE_BYTES bytes. (512 bits for a 64 bytes cache line) > > If you check commit 0c9e63fd38a2fb2181668a0cdd622a3c23cfd567, > (http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=com >mit;h=0c9e63fd38a2fb2181668a0cdd622a3c23cfd567 ) you'll find this comment of > mine : > > 3) Reduce size of allocated fdset. Currently two full pages are > allocated, that is 32768 bits on x86 for example, and way too much. The > minimum is now L1_CACHE_BYTES. > > This minimum is mandatory to be sure two tasks wont share the same cache > line to store their fdset (and possibly do lot of cache line ping pongs) Good point. This should be easy to fix -- we can simply bump up the allocation 'nr' when calling alloc_fdmem() for the fdset. Since we won't cross a page size, the rest of the code will still stay the same. I'll code this up once I track down why other folks are experiencing oopses. > Eric -- Vadim Lobanov