From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751353AbdKUPuB (ORCPT ); Tue, 21 Nov 2017 10:50:01 -0500 Received: from mail-wm0-f66.google.com ([74.125.82.66]:45695 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750794AbdKUPt7 (ORCPT ); Tue, 21 Nov 2017 10:49:59 -0500 X-Google-Smtp-Source: AGs4zMYTTAbc9TOqyk1YYRpAaYK+44bIKuLAa5wFfxRjYuifCeLdWuDJHKIRnuBsR1Sb/uI6A425LA== Reply-To: christian.koenig@amd.com Subject: Re: [PATCH] reservation: don't wait when timeout=0 To: Rob Clark , Chris Wilson Cc: "linaro-mm-sig@lists.linaro.org" , Linux Kernel Mailing List , "dri-devel@lists.freedesktop.org" , "linux-media@vger.kernel.org" References: <20171121140850.23401-1-robdclark@gmail.com> <151127508188.436.3320065005004428970@mail.alporthouse.com> From: =?UTF-8?Q?Christian_K=c3=b6nig?= Message-ID: <83c7c887-0d40-69b5-2ad2-67d0af6eda71@gmail.com> Date: Tue, 21 Nov 2017 16:49:55 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am 21.11.2017 um 15:59 schrieb Rob Clark: > On Tue, Nov 21, 2017 at 9:38 AM, Chris Wilson wrote: >> Quoting Rob Clark (2017-11-21 14:08:46) >>> If we are testing if a reservation object's fences have been >>> signaled with timeout=0 (non-blocking), we need to pass 0 for >>> timeout to dma_fence_wait_timeout(). >>> >>> Plus bonus spelling correction. >>> >>> Signed-off-by: Rob Clark >>> --- >>> drivers/dma-buf/reservation.c | 11 +++++++++-- >>> 1 file changed, 9 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c >>> index dec3a815455d..71f51140a9ad 100644 >>> --- a/drivers/dma-buf/reservation.c >>> +++ b/drivers/dma-buf/reservation.c >>> @@ -420,7 +420,7 @@ EXPORT_SYMBOL_GPL(reservation_object_get_fences_rcu); >>> * >>> * RETURNS >>> * Returns -ERESTARTSYS if interrupted, 0 if the wait timed out, or >>> - * greater than zer on success. >>> + * greater than zero on success. >>> */ >>> long reservation_object_wait_timeout_rcu(struct reservation_object *obj, >>> bool wait_all, bool intr, >>> @@ -483,7 +483,14 @@ long reservation_object_wait_timeout_rcu(struct reservation_object *obj, >>> goto retry; >>> } >>> >>> - ret = dma_fence_wait_timeout(fence, intr, ret); >>> + /* >>> + * Note that dma_fence_wait_timeout() will return 1 if >>> + * the fence is already signaled, so in the wait_all >>> + * case when we go through the retry loop again, ret >>> + * will be greater than 0 and we don't want this to >>> + * cause _wait_timeout() to block >>> + */ >>> + ret = dma_fence_wait_timeout(fence, intr, timeout ? ret : 0); >> One should ask if we should just fix the interface to stop returning >> incorrect results (stop "correcting" a completion with 0 jiffies remaining >> as 1). A timeout can be distinguished by -ETIME (or your pick of errno). > perhaps -EBUSY, if we go that route (although maybe it should be a > follow-on patch, this one is suitable for backport to stable/lts if > one should so choose..) > > I think current approach was chosen to match schedule_timeout() and > other such functions that take a timeout in jiffies. Not making a > judgement on whether that is a good or bad reason.. We intentionally switched away from that to be in sync with the wait_event_* interface. Returning 1 when a function with a zero timeout succeeds is actually quite common in the kernel. Regards, Christian. > BR, > -R > >> -Chris > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel