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Subject: Re: [LKP] [drm/mgag200] 90f479ae51: vm-scalability.median -18.8%
 regression
To:     Feng Tang <feng.tang@intel.com>, Daniel Vetter <daniel@ffwll.ch>
Cc:     Stephen Rothwell <sfr@canb.auug.org.au>,
        Rong Chen <rong.a.chen@intel.com>,
        =?UTF-8?Q?Michel_D=c3=a4nzer?= <michel@daenzer.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>, LKP <lkp@01.org>
References: <64d41701-55a4-e526-17ae-8936de4bc1ef@suse.de>
 <20190824051605.GA63850@shbuild999.sh.intel.com>
 <1b897bfe-fd40-3ae3-d867-424d1fc08c44@suse.de>
 <d114b0b6-6b64-406e-6c3f-a8b8d5502413@intel.com>
 <44029e80-ba00-8246-dec0-fda122d53f5e@suse.de>
 <90e78ce8-d46a-5154-c324-a05aa1743c98@intel.com>
 <2e1b4d65-d477-f571-845d-fa0a670859af@suse.de>
 <20190904062716.GC5541@shbuild999.sh.intel.com>
 <72c33bf1-9184-e24a-c084-26d9c8b6f9b7@suse.de>
 <CAKMK7uGdOtyDHZMSzY8J45bX57EFKo=DWNUi+WL+GVOzoBpUhw@mail.gmail.com>
 <20190904083558.GD5541@shbuild999.sh.intel.com>
From:   Thomas Zimmermann <tzimmermann@suse.de>
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Message-ID: <33d3ce15-6221-bd96-3f26-b710e4da6b1a@suse.de>
Date:   Wed, 4 Sep 2019 10:43:40 +0200
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From: Thomas Zimmermann <tzimmermann@suse.de>
To: Feng Tang <feng.tang@intel.com>, Daniel Vetter <daniel@ffwll.ch>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>, Rong Chen
 <rong.a.chen@intel.com>, =?UTF-8?Q?Michel_D=c3=a4nzer?=
 <michel@daenzer.net>,
 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
 dri-devel <dri-devel@lists.freedesktop.org>, LKP <lkp@01.org>
Message-ID: <33d3ce15-6221-bd96-3f26-b710e4da6b1a@suse.de>
Subject: Re: [LKP] [drm/mgag200] 90f479ae51: vm-scalability.median -18.8%
 regression
References: <64d41701-55a4-e526-17ae-8936de4bc1ef@suse.de>
 <20190824051605.GA63850@shbuild999.sh.intel.com>
 <1b897bfe-fd40-3ae3-d867-424d1fc08c44@suse.de>
 <d114b0b6-6b64-406e-6c3f-a8b8d5502413@intel.com>
 <44029e80-ba00-8246-dec0-fda122d53f5e@suse.de>
 <90e78ce8-d46a-5154-c324-a05aa1743c98@intel.com>
 <2e1b4d65-d477-f571-845d-fa0a670859af@suse.de>
 <20190904062716.GC5541@shbuild999.sh.intel.com>
 <72c33bf1-9184-e24a-c084-26d9c8b6f9b7@suse.de>
 <CAKMK7uGdOtyDHZMSzY8J45bX57EFKo=DWNUi+WL+GVOzoBpUhw@mail.gmail.com>
 <20190904083558.GD5541@shbuild999.sh.intel.com>
In-Reply-To: <20190904083558.GD5541@shbuild999.sh.intel.com>

--GAqvzYwfBSRNT5wxc8MZTQlopx9rsHEt8
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Hi

Am 04.09.19 um 10:35 schrieb Feng Tang:
> Hi Daniel,
>=20
> On Wed, Sep 04, 2019 at 10:11:11AM +0200, Daniel Vetter wrote:
>> On Wed, Sep 4, 2019 at 8:53 AM Thomas Zimmermann <tzimmermann@suse.de>=
 wrote:
>>>
>>> Hi
>>>
>>> Am 04.09.19 um 08:27 schrieb Feng Tang:
>>>>> Thank you for testing. But don't get too excited, because the patch=

>>>>> simulates a bug that was present in the original mgag200 code. A
>>>>> significant number of frames are simply skipped. That is apparently=
 the
>>>>> reason why it's faster.
>>>>
>>>> Thanks for the detailed info, so the original code skips time-consum=
ing
>>>> work inside atomic context on purpose. Is there any space to optmise=
 it?
>>>> If 2 scheduled update worker are handled at almost same time, can on=
e be
>>>> skipped?
>>>
>>> To my knowledge, there's only one instance of the worker. Re-scheduli=
ng
>>> the worker before a previous instance started, will not create a seco=
nd
>>> instance. The worker's instance will complete all pending updates. So=
 in
>>> some way, skipping workers already happens.
>>
>> So I think that the most often fbcon update from atomic context is the=

>> blinking cursor. If you disable that one you should be back to the old=

>> performance level I think, since just writing to dmesg is from process=

>> context, so shouldn't change.
>=20
> Hmm, then for the old driver, it should also do the most update in
> non-atomic context?=20
>=20
> One other thing is, I profiled that updating a 3MB shadow buffer needs
> 20 ms, which transfer to 150 MB/s bandwidth. Could it be related with
> the cache setting of DRM shadow buffer? say the orginal code use a
> cachable buffer?
>=20
>=20
>>
>> https://unix.stackexchange.com/questions/3759/how-to-stop-cursor-from-=
blinking
>>
>> Bunch of tricks, but tbh I haven't tested them.
>=20
> Thomas has suggested to disable curson by
> 	echo 0 > /sys/devices/virtual/graphics/fbcon/cursor_blink
>=20
> We tried that way, and no change for the performance data.

There are several ways of disabling the cursor. On my test system, I ente=
red

  tput civis

before the test and got better performance. Did you try this as well?

Best regards
Thomas

>=20
> Thanks,
> Feng
>=20
>>
>> In any case, I still strongly advice you don't print anything to dmesg=

>> or fbcon while benchmarking, because dmesg/printf are anything but
>> fast, especially if a gpu driver is involved. There's some efforts to
>> make the dmesg/printk side less painful (untangling the console_lock
>> from printk), but fundamentally printing to the gpu from the kernel
>> through dmesg/fbcon won't be cheap. It's just not something we
>> optimize beyond "make sure it works for emergencies".
>> -Daniel
>>
>>>
>>> Best regards
>>> Thomas
>>>
>>>>
>>>> Thanks,
>>>> Feng
>>>>
>>>>>
>>>>> Best regards
>>>>> Thomas
>>>> _______________________________________________
>>>> dri-devel mailing list
>>>> dri-devel@lists.freedesktop.org
>>>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>>>>
>>>
>>> --
>>> Thomas Zimmermann
>>> Graphics Driver Developer
>>> SUSE Linux GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany
>>> GF: Felix Imend=C3=B6rffer, Mary Higgins, Sri Rasiah
>>> HRB 21284 (AG N=C3=BCrnberg)
>>>
>>> _______________________________________________
>>> dri-devel mailing list
>>> dri-devel@lists.freedesktop.org
>>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>>
>>
>>
>> --=20
>> Daniel Vetter
>> Software Engineer, Intel Corporation
>> +41 (0) 79 365 57 48 - http://blog.ffwll.ch

--=20
Thomas Zimmermann
Graphics Driver Developer
SUSE Linux GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany
GF: Felix Imend=C3=B6rffer, Mary Higgins, Sri Rasiah
HRB 21284 (AG N=C3=BCrnberg)


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