Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752983Ab1CPRRm (ORCPT ); Wed, 16 Mar 2011 13:17:42 -0400 Received: from smtp-out.google.com ([216.239.44.51]:26285 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751688Ab1CPRRg (ORCPT ); Wed, 16 Mar 2011 13:17:36 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=date:from:x-x-sender:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version:content-type; b=t1SauZGM3HM0BN4sYnstRAunh9ng91rqN8HwRalfPCmnt86OjIV8FbN3GNBCvDzzrK LYLqDIl6YcnIo+Pt1i4g== Date: Wed, 16 Mar 2011 10:17:19 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@sister.anvils To: George Spelvin cc: penberg@cs.helsinki.fi, herbert@gondor.hengli.com.au, mpm@selenic.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/8] drivers/random: Cache align ip_random better In-Reply-To: <20110316022804.27679.qmail@science.horizon.com> Message-ID: References: <20110316022804.27679.qmail@science.horizon.com> User-Agent: Alpine 2.00 (LSU 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1327 Lines: 36 On Sun, 13 Mar 2011, George Spelvin wrote: > Cache aligning the secret[] buffer makes copying from it infinitesimally > more efficient. > --- > drivers/char/random.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/drivers/char/random.c b/drivers/char/random.c > index 72a4fcb..4bcc4f2 100644 > --- a/drivers/char/random.c > +++ b/drivers/char/random.c > @@ -1417,8 +1417,8 @@ static __u32 twothirdsMD4Transform(__u32 const buf[4], __u32 const in[12]) > #define HASH_MASK ((1 << HASH_BITS) - 1) > > static struct keydata { > - __u32 count; /* already shifted to the final position */ > __u32 secret[12]; > + __u32 count; /* already shifted to the final position */ > } ____cacheline_aligned ip_keydata[2]; > > static unsigned int ip_cnt; I'm intrigued: please educate me. On what architectures does cache- aligning a 48-byte buffer (previously offset by 4 bytes) speed up copying from it, and why? Does the copying involve 8-byte or 16-byte instructions that benefit from that alignment, rather than cacheline alignment? Thanks, Hugh -- 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/