From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753328AbcEBJbW (ORCPT ); Mon, 2 May 2016 05:31:22 -0400 Received: from mga02.intel.com ([134.134.136.20]:47399 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752459AbcEBJbM (ORCPT ); Mon, 2 May 2016 05:31:12 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.24,566,1455004800"; d="scan'208";a="944309018" Date: Mon, 2 May 2016 15:07:12 +0530 From: Vinod Koul To: Kuninori Morimoto Cc: Geert Uytterhoeven , Laurent Pinchart , sakato , OSD2 ML , dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] dma: rcar-dmac: use list_add() on rcar_dmac_desc_put() Message-ID: <20160502093712.GE2274@localhost> References: <8760w7xq3n.wl%kuninori.morimoto.gx@renesas.com> <874mbrxnft.wl%kuninori.morimoto.gx@renesas.com> <1645988.6VIRltF7C5@avalon> <87r3dywh6u.wl%kuninori.morimoto.gx@renesas.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87r3dywh6u.wl%kuninori.morimoto.gx@renesas.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 22, 2016 at 01:50:04AM +0000, Kuninori Morimoto wrote: > > From: Kuninori Morimoto > > Current rcar_dmac_desc_put() is using list_add_tail() in order to > push used descriptor to list of free descriptors, and next DMA transfer > try to reuse it from this list. But because it is using *_tail(), > this reuse effect can't be obtained without using all of them. > For a longer-term solution, we should allocate hardware descriptors > using GFP_KERNEL instead of GFP_NOWAIT, but it is difficult today. > This patch uses list_add() instead of list_add_tail() for short-term > solution. So how does reuse case help by not moving the descriptor to tail. Also you are not reusing descriptor, you are reusing a descriptor memory, these are two different things. Lastly how does this help? Something doesn't seem right > > Signed-off-by: Kuninori Morimoto > --- > drivers/dma/sh/rcar-dmac.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c > index 02b86c6..616c63a 100644 > --- a/drivers/dma/sh/rcar-dmac.c > +++ b/drivers/dma/sh/rcar-dmac.c > @@ -519,7 +519,7 @@ static void rcar_dmac_desc_put(struct rcar_dmac_chan *chan, > > spin_lock_irqsave(&chan->lock, flags); > list_splice_tail_init(&desc->chunks, &chan->desc.chunks_free); > - list_add_tail(&desc->node, &chan->desc.free); > + list_add(&desc->node, &chan->desc.free); > spin_unlock_irqrestore(&chan->lock, flags); > } > -- ~Vinod