Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757892AbYCNAG2 (ORCPT ); Thu, 13 Mar 2008 20:06:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751631AbYCNAGV (ORCPT ); Thu, 13 Mar 2008 20:06:21 -0400 Received: from wr-out-0506.google.com ([64.233.184.230]:49105 "EHLO wr-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751477AbYCNAGU (ORCPT ); Thu, 13 Mar 2008 20:06:20 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:sender:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references:x-google-sender-auth; b=B8agPN4P/FWtiuivTsQEB4ljblGoB5pZJVxjuQdszCF56DkquURhO1zOD4pKIb+ugJEPjFjZ50MCKIVU508sk5LZYxDneNlYnVZSbSxcdUJkTuNlIGLpspYTVHCxRd2To8cYeNjx3a7CTP5+yamXJuvyPUH7JzOzlAAFwZ8lA6M= Message-ID: Date: Thu, 13 Mar 2008 17:06:19 -0700 From: "Dan Williams" To: "Olof Johansson" Subject: Re: [PATCH] pasemi_dma: Driver for PA Semi PWRficient on-chip DMAengine Cc: linuxppc-dev@ozlabs.org, pasemi-linux@ozlabs.org, "Nelson, Shannon" , linux-kernel@vger.kernel.org, hskinnemoen@atmel.com In-Reply-To: <20080313231442.GA4639@lixom.net> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <20080306233900.GA3969@lixom.net> <1205255051.26723.19.camel@dwillia2-linux.ch.intel.com> <20080313195431.GA1449@lixom.net> <20080313231442.GA4639@lixom.net> X-Google-Sender-Auth: 4f1e4d7347b5cbc4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1760 Lines: 46 On Thu, Mar 13, 2008 at 4:14 PM, Olof Johansson wrote: > > Dummy descriptors that do nothing but cause an interrupt is the intent. > > Well, it'd be slightly more efficient to do add the interrupt attribute > to the last issued descriptor when it's known in advance. If the > underlying driver doesn't support it, adding a separate descriptor would > be a good fallback. > When it is known in advance the interrupt attribute *is* set, otherwise the descriptor may already be in flight. > Anyway, this isn't likely to be a performance bottleneck. If it turns > out to be, I'll refactor it and submit patches. > Would not hurt to have another pair of eyes on this part of the code. A rewrite of the channel switch mechanism is currently pending in async_tx.git#upstream. [..] > > > Can't do that if it's called both from the polling as well as the IRQ > > > context, it'd need to hold off irqs. I.e. once I add the DMA_INTERRUPT > > > support it will be needed. > > > > > > > ...do it in a tasklet. > > Why? That just adds overhead and latency. > The original ioat_dma code used nothing heavier than spin_lock_bh. Async_tx now assumes that local_bh_disable prevents races with any channel's cleanup routine. Clients can place the same kind of code in an async_tx callback as they would in a timer callback. The assumption is that code using async_tx can afford its extra overhead, which is true for raid. This is also why you don't see async_memcpy calls in net_dma. -- Dan -- 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/