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=-17.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, 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 30937C433F5 for ; Thu, 23 Sep 2021 17:43:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1B85C60F4C for ; Thu, 23 Sep 2021 17:43:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242582AbhIWRpA (ORCPT ); Thu, 23 Sep 2021 13:45:00 -0400 Received: from mail.kernel.org ([198.145.29.99]:48196 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233669AbhIWRpA (ORCPT ); Thu, 23 Sep 2021 13:45:00 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id C840B60F4C; Thu, 23 Sep 2021 17:43:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1632419008; bh=2pB6+rQ1KDZ58hG85EpwUaTjBgEVnhSiiN/dICRDX0I=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=TcqGwPZ2yJSYhj+2XwfJI9SKh/1wdSZcDO4YrDj5FYSI1KJ3D1HsiUl+Ufj+vAMD1 Ny4uX2qOLkAYLBUmuIeuUjIDC/KM99atliXBgXo7Xw9IJNN3KUnY51rgqVJRYngEmo Dvj4kZH+UQga8MbdrzzoE0+GFoVAFuwQKOpJK9qw= Date: Thu, 23 Sep 2021 19:43:26 +0200 From: Greg KH To: jeyr@codeaurora.org Cc: linux-arm-msm@vger.kernel.org, srinivas.kandagatla@linaro.org, linux-kernel@vger.kernel.org, fastrpc.upstream@qti.qualcomm.com Subject: Re: [PATCH] misc: fastrpc: copy to user only for non-DMA-BUF heap buffers Message-ID: References: <1632386272-18139-1-git-send-email-jeyr@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org On Thu, Sep 23, 2021 at 03:54:15PM +0530, jeyr@codeaurora.org wrote: > On 2021-09-23 14:19, Greg KH wrote: > > On Thu, Sep 23, 2021 at 02:07:52PM +0530, Jeya R wrote: > > > fastrpc_put_args is copying all the output buffers to user. For large > > > number of output context buffers, this might cause performance > > > degradation. Copying is not needed for DMA-BUF heap buffers. > > > > What does "performance degradation" really mean? > > Unnecessary copying for large number of buffers would cause some > additional time which would get added to overall fastrpc call cost. > > > > > > > > > Signed-off-by: Jeya R > > > --- > > > drivers/misc/fastrpc.c | 18 ++++++++++-------- > > > 1 file changed, 10 insertions(+), 8 deletions(-) > > > > > > diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c > > > index beda610..536eabf 100644 > > > --- a/drivers/misc/fastrpc.c > > > +++ b/drivers/misc/fastrpc.c > > > @@ -890,15 +890,17 @@ static int fastrpc_put_args(struct > > > fastrpc_invoke_ctx *ctx, > > > inbufs = REMOTE_SCALARS_INBUFS(ctx->sc); > > > > > > for (i = inbufs; i < ctx->nbufs; ++i) { > > > - void *src = (void *)(uintptr_t)rpra[i].pv; > > > - void *dst = (void *)(uintptr_t)ctx->args[i].ptr; > > > - u64 len = rpra[i].len; > > > + if (!ctx->maps[i]) { > > > + void *src = (void *)(uintptr_t)rpra[i].pv; > > > + void *dst = (void *)(uintptr_t)ctx->args[i].ptr; > > > > uintptr_t is not a kernel variable type. Please use the real kernel > > type for this as you are touching these lines. > > > > Sure, thanks for pointing this. Will update this in the next patch. > > > > + u64 len = rpra[i].len; > > > > > > - if (!kernel) { > > > - if (copy_to_user((void __user *)dst, src, len)) > > > - return -EFAULT; > > > - } else { > > > - memcpy(dst, src, len); > > > + if (!kernel) { > > > + if (copy_to_user((void __user *)dst, src, len)) > > > + return -EFAULT; > > > + } else { > > > + memcpy(dst, src, len); > > > + } > > > > So you were copying buffers that didn't need to be copied? So you are > > now doing less work? Or is this fixing a bug where you were copying > > things that you should not have been copying? > > > > What commit does this fix? Does this need to go to the stable kernel > > trees? > > > > Yes, not all buffer needs to be copied. This change would avoid unnecessary > copying of buffers. Not adding fix tag as it's not exactly fixing any bug. > This should go to stable kernel trees. If it's not fixing a bug, why should it go into the stable trees?