From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C11E8C4320A for ; Wed, 4 Aug 2021 09:31:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A394060FC4 for ; Wed, 4 Aug 2021 09:31:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236578AbhHDJbo (ORCPT ); Wed, 4 Aug 2021 05:31:44 -0400 Received: from smtp-out1.suse.de ([195.135.220.28]:40182 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230436AbhHDJbn (ORCPT ); Wed, 4 Aug 2021 05:31:43 -0400 Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id B402D221B5; Wed, 4 Aug 2021 09:31:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1628069490; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/CL90sbdhCGnwPijnIZMVO1l7TdCtzuZFibOtSaIO3g=; b=vnk1T4jqLsR2415kEzCvuSnxDm09j7/RRja16DAosTFHalxLxgBIT08YF2mzYveQ3XZwkj SZbcJoCqou/sJrO8c+aIWy4nwuoTYXf1GDwnr878/S8VKAdzm27I+VucnzXVtAHcavNqjm NATc5+6EH38AKumeHld3XpKjGUZC1pM= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1628069490; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/CL90sbdhCGnwPijnIZMVO1l7TdCtzuZFibOtSaIO3g=; b=ebEeoWXlX+Pg1i8Oo1rgxE/sHDeHH1cw7yTNQ9BxF+BFQZUdj5DGfbEoCrPzTm6uPjP9bv 1gWXYZsAFHlS/nBg== Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap1.suse-dmz.suse.de (Postfix) with ESMTPS id 851841338E; Wed, 4 Aug 2021 09:31:30 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap1.suse-dmz.suse.de with ESMTPSA id rVNrHnJeCmFMbQAAGKfGzw (envelope-from ); Wed, 04 Aug 2021 09:31:30 +0000 Date: Wed, 4 Aug 2021 11:31:29 +0200 From: David Disseldorp To: linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org Cc: Matthew Wilcox , Al Viro Subject: Re: [PATCH RESEND 1/3] initramfs: move unnecessary memcmp from hot path Message-ID: <20210804113129.60848be6@suse.de> In-Reply-To: <20210721115153.28620-1-ddiss@suse.de> References: <20210721115153.28620-1-ddiss@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Ping, any feedback on this change? I think it's a no brainer, but for kicks I ran a few unrealistic micro benchmarks on my laptop. Extraction time for a cpio image with 1M+ directories improved by 5ms (pre: 14.614s, post: 14.609s), when averaged across 20 runs of: qemu-system-x86_64 -machine accel=kvm -smp cpus=1 -m 10240 \ -kernel ~/linux/arch/x86/boot/bzImage \ -initrd ./initrds/gen_cpio.out \ -append "initramfs_async=0 console=ttyS0 panic=0" -nographic \ | awk '/Trying to unpack rootfs/ {start_ts = $2}; /Freeing initrd memory/ {end_ts = $2} END {printf "%f\n", end_ts - start_ts}' Cheers, David On Wed, 21 Jul 2021 13:51:51 +0200, David Disseldorp wrote: > do_header() is called for each cpio entry and first checks for "newc" > magic before parsing further. The magic check includes a special case > error message if POSIX.1 ASCII (cpio -H odc) magic is detected. This > special case POSIX.1 check needn't be done in the hot path, so move it > under the non-newc-magic error path. > > Signed-off-by: David Disseldorp > --- > init/initramfs.c | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > > diff --git a/init/initramfs.c b/init/initramfs.c > index af27abc59643..f01590cefa2d 100644 > --- a/init/initramfs.c > +++ b/init/initramfs.c > @@ -256,12 +256,11 @@ static int __init do_collect(void) > > static int __init do_header(void) > { > - if (memcmp(collected, "070707", 6)==0) { > - error("incorrect cpio method used: use -H newc option"); > - return 1; > - } > if (memcmp(collected, "070701", 6)) { > - error("no cpio magic"); > + if (memcmp(collected, "070707", 6) == 0) > + error("incorrect cpio method used: use -H newc option"); > + else > + error("no cpio magic"); > return 1; > } > parse_header(collected);