Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Reply-To: christian.koenig@amd.com
Subject: Re: [PATCH] reservation: don't wait when timeout=0
To:     Rob Clark <robdclark@gmail.com>,
        Chris Wilson <chris@chris-wilson.co.uk>
Cc:     "linaro-mm-sig@lists.linaro.org" <linaro-mm-sig@lists.linaro.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        "linux-media@vger.kernel.org" <linux-media@vger.kernel.org>
References: <20171121140850.23401-1-robdclark@gmail.com>
 <151127508188.436.3320065005004428970@mail.alporthouse.com>
 <CAF6AEGuo=e8rOnLHX3rL9qGTenSRDO2D=S7GQs9rq+=5SVqS0g@mail.gmail.com>
From:   =?UTF-8?Q?Christian_K=c3=b6nig?= <ckoenig.leichtzumerken@gmail.com>
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: <CAF6AEGuo=e8rOnLHX3rL9qGTenSRDO2D=S7GQs9rq+=5SVqS0g@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Content-Language: en-US
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Am 21.11.2017 um 15:59 schrieb Rob Clark:
> On Tue, Nov 21, 2017 at 9:38 AM, Chris Wilson <chris@chris-wilson.co.uk> 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 <robdclark@gmail.com>
>>> ---
>>>   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


From 1584688173487425314@xxx Tue Nov 21 15:00:10 +0000 2017
X-GM-THRID: 1584685078993396088
X-Gmail-Labels: Inbox,Category Forums,HistoricalUnread