Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752753AbZLADIO (ORCPT ); Mon, 30 Nov 2009 22:08:14 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752305AbZLADIM (ORCPT ); Mon, 30 Nov 2009 22:08:12 -0500 Received: from ozlabs.org ([203.10.76.45]:53736 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752107AbZLADIL (ORCPT ); Mon, 30 Nov 2009 22:08:11 -0500 From: Rusty Russell To: Matt Mackall Subject: Re: [PATCH 1/2] hw_random: core updates to allow more efficient drivers Date: Tue, 1 Dec 2009 13:38:15 +1030 User-Agent: KMail/1.12.2 (Linux/2.6.31-15-generic; KDE/4.3.2; i686; ; ) Cc: Ian Molton , linux-kernel@vger.kernel.org, Herbert Xu , Jeff Garzik References: <1259177252.2858.17.camel@calx> <4B139E3D.1020905@collabora.co.uk> <1259606656.29740.48.camel@calx> In-Reply-To: <1259606656.29740.48.camel@calx> MIME-Version: 1.0 Content-Type: Text/Plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <200912011338.15763.rusty@rustcorp.com.au> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1283 Lines: 32 On Tue, 1 Dec 2009 05:14:16 am Matt Mackall wrote: > On Mon, 2009-11-30 at 10:28 +0000, Ian Molton wrote: > > Rusty Russell wrote: > > > > > And might as well just #defube RNG_BUFFSIZE SMP_CACHE_BYTES (or use > > > SMP_CACHE_BYTES here and sizeof() elsewhere). > > > > This can lead to a rather small (4 byte) buffer on some systems, however > > I don't know if in practice a tiny buffer or a big one would be better > > for performance on those machines. I guess if its a problem someone can > > patch the code to allocate a minimum of (say) 16 bytes in future... > > Hmmm, I think this was bad advice from Rusty. Me too. But really, it's because we're using cacheline alignment as a proxy for something else, and it's not a good fit. But we're bikeshedding, so apply or revert. /* A buffer which can hold any fundamental type: drivers are fussy. */ static u8 rng_buffer[SMP_CACHE_BYTES < 8 ? 8 : SMP_CACHE_BYTES] __cacheline_aligned; Either way, both patches: Acked-by: Rusty Russell Thanks, Rusty. -- 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/