Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964790AbWJJRMy (ORCPT ); Tue, 10 Oct 2006 13:12:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750996AbWJJRMy (ORCPT ); Tue, 10 Oct 2006 13:12:54 -0400 Received: from pfx2.jmh.fr ([194.153.89.55]:44203 "EHLO pfx2.jmh.fr") by vger.kernel.org with ESMTP id S1750989AbWJJRMx (ORCPT ); Tue, 10 Oct 2006 13:12:53 -0400 From: Eric Dumazet To: Vadim Lobanov Subject: Re: [PATCH 2/5] fdtable: Make fdarray and fdsets equal in size. Date: Tue, 10 Oct 2006 19:12:56 +0200 User-Agent: KMail/1.9.4 Cc: akpm@osdl.org, linux-kernel@vger.kernel.org References: <200610052151.04490.vlobanov@speakeasy.net> In-Reply-To: <200610052151.04490.vlobanov@speakeasy.net> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200610101912.56280.dada1@cosmosbay.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1586 Lines: 43 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=commit;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) Eric - 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/