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Wed, 11 Jun 2025 23:18:02 +0000 Received: from SN6PR02MB4157.namprd02.prod.outlook.com ([fe80::cedd:1e64:8f61:b9df]) by SN6PR02MB4157.namprd02.prod.outlook.com ([fe80::cedd:1e64:8f61:b9df%4]) with mapi id 15.20.8835.018; Wed, 11 Jun 2025 23:18:02 +0000 From: Michael Kelley To: Thomas Zimmermann , Simona Vetter CC: David Hildenbrand , "simona@ffwll.ch" , "deller@gmx.de" , "haiyangz@microsoft.com" , "kys@microsoft.com" , "wei.liu@kernel.org" , "decui@microsoft.com" , "akpm@linux-foundation.org" , "weh@microsoft.com" , "hch@lst.de" , "dri-devel@lists.freedesktop.org" , "linux-fbdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-hyperv@vger.kernel.org" , "linux-mm@kvack.org" Subject: RE: [PATCH v3 3/4] fbdev/deferred-io: Support contiguous kernel memory framebuffers Thread-Topic: [PATCH v3 3/4] fbdev/deferred-io: Support contiguous kernel memory framebuffers Thread-Index: AQHby/4dA8oNLnhKakm3U+ZOuvHFDrPvrtEAgAEJQeCAAFCFAIAAuDlwgAD4GoCAAG28AIAAbZyQgAEy0YCAAB38UIAJ0FOA Date: Wed, 11 Jun 2025 23:18:02 +0000 Message-ID: References: <20250523161522.409504-1-mhklinux@outlook.com> <20250523161522.409504-4-mhklinux@outlook.com> <9a93813c-4d7c-45ef-b5a2-0ad37e7a078a@suse.de> <154aa365-0e27-458c-b801-62fd1cbfa169@suse.de> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-publictraffictype: Email x-ms-traffictypediagnostic: SN6PR02MB4157:EE_|CH2PR02MB6553:EE_ x-ms-office365-filtering-correlation-id: 8daafcc1-e114-4c4f-5805-08dda93e36a1 x-ms-exchange-slblob-mailprops: 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 x-microsoft-antispam: BCL:0;ARA:14566002|461199028|15080799009|19110799006|41001999006|8062599006|8060799009|1602099012|52005399003|3412199025|4302099013|440099028|10035399007|102099032; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: SN6PR02MB4157.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-RMS-PersistedConsumerOrg: 00000000-0000-0000-0000-000000000000 X-MS-Exchange-CrossTenant-Network-Message-Id: 8daafcc1-e114-4c4f-5805-08dda93e36a1 X-MS-Exchange-CrossTenant-originalarrivaltime: 11 Jun 2025 23:18:02.5508 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 84df9e7f-e9f6-40af-b435-aaaaaaaaaaaa X-MS-Exchange-CrossTenant-rms-persistedconsumerorg: 00000000-0000-0000-0000-000000000000 X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH2PR02MB6553 X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 5659E40004 X-Stat-Signature: tdbs1oxhck1h3gdcjfn1ym4pr9d4ag69 X-HE-Tag: 1749683887-436144 X-HE-Meta: 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 4OZJ9fWg 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Michael Kelley Sent: Thursday, June 5, 2025 10:39 AM >=20 > From: Thomas Zimmermann Sent: Thursday, June 5, 202= 5 > 8:36 AM > > > > Hi > > > > Am 04.06.25 um 23:43 schrieb Michael Kelley: > > [...] > > > Nonetheless, there's an underlying issue. A main cause of the differe= nce > > > is the number of messages to Hyper-V to update dirty regions. With > > > hyperv_fb using deferred I/O, the messages are limited 20/second, so > > > the total number of messages to Hyper-V is about 480. But hyperv_drm > > > appears to send 3 messages to Hyper-V for each line of output, or a t= otal of > > > about 3,000,000 messages (~90K/second). That's a lot of additional lo= ad > > > on the Hyper-V host, and it adds the 10 seconds of additional elapsed > > > time seen in the guest. There also this ugly output in dmesg because = the > > > ring buffer for sending messages to the Hyper-V host gets full -- Hyp= er-V > > > doesn't always keep up, at least not on my local laptop where I'm > > > testing: > > > > > > [12574.327615] hyperv_drm 5620e0c7-8062-4dce-aeb7-520c7ef76171: [drm] > > *ERROR* Unable to send packet via vmbus; error -11 > > > [12574.327684] hyperv_drm 5620e0c7-8062-4dce-aeb7-520c7ef76171: [drm] > > *ERROR* Unable to send packet via vmbus; error -11 > > > [12574.327760] hyperv_drm 5620e0c7-8062-4dce-aeb7-520c7ef76171: [drm] > > *ERROR* Unable to send packet via vmbus; error -11 > > > [12574.327841] hyperv_drm 5620e0c7-8062-4dce-aeb7-520c7ef76171: [drm] > > *ERROR* Unable to send packet via vmbus; error -11 > > > [12597.016128] hyperv_sendpacket: 6211 callbacks suppressed > > > [12597.016133] hyperv_drm 5620e0c7-8062-4dce-aeb7-520c7ef76171: [drm] > > *ERROR* Unable to send packet via vmbus; error -11 > > > [12597.016172] hyperv_drm 5620e0c7-8062-4dce-aeb7-520c7ef76171: [drm] > > *ERROR* Unable to send packet via vmbus; error -11 > > > [12597.016220] hyperv_drm 5620e0c7-8062-4dce-aeb7-520c7ef76171: [drm] > > *ERROR* Unable to send packet via vmbus; error -11 > > > [12597.016267] hyperv_drm 5620e0c7-8062-4dce-aeb7-520c7ef76171: [drm] > > *ERROR* Unable to send packet via vmbus; error -11 > > > > > > hyperv_drm could be fixed to not output the ugly messages, but there'= s > > > still the underlying issue of overrunning the ring buffer, and excess= ively > > > hammering on the host. If we could get hyperv_drm doing deferred I/O,= I > > > would feel much better about going full-on with deprecating hyperv_fb= . > > > > I try to address the problem with the patches at > > > > https://lore.kernel.org/dri-devel/20250605152637.98493-1- > tzimmermann@suse.de/ > > > > Testing and feedback is much appreciated. > > >=20 > Nice! >=20 > I ran the same test case with your patches, and everything works well. Th= e > hyperv_drm numbers are now pretty much the same as the hyperv_fb > numbers for both elapsed time and system CPU time -- within a few percent= . > For hyperv_drm, there's no longer a gap in the elapsed time and system > CPU time. No errors due to the guest-to-host ring buffer being full. Tota= l > messages to Hyper-V for hyperv_drm are now a few hundred instead of 3M. > The hyperv_drm message count is still a little higher than for hyperv_fb, > presumably because the simulated vblank rate in hyperv_drm is higher than > the 20 Hz rate used by hyperv_fb deferred I/O. But the overall numbers ar= e > small enough that the difference is in the noise. Question: what is the d= efault > value for the simulated vblank rate? Just curious ... >=20 FYI, I'm seeing this message occasionally when running with your simulated vblank code and hyperv_drm: [90920.128278] hyperv_drm 5620e0c7-8062-4dce-aeb7-520c7ef76171: [drm] vblan= k timer overrun "Occasionally" is about a dozen occurrences over the last day or so. I can'= t yet correlate to any particular activity in the VM. The graphics console ha= s not been very busy. Michael