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Thu, 5 Jun 2025 17:38:57 +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 15.20.8813.016; Thu, 5 Jun 2025 17:38:57 +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+ZOuvHFDrPvrtEAgAEJQeCAAFCFAIAAuDlwgAD4GoCAAG28AIAAbZyQgAEy0YCAAB38UA== Date: Thu, 5 Jun 2025 17:38:57 +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: <154aa365-0e27-458c-b801-62fd1cbfa169@suse.de> 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_|MN6PR02MB10728:EE_ x-ms-office365-filtering-correlation-id: 7570987c-c0e0-4b12-73bd-08dda457d99e x-ms-exchange-slblob-mailprops: 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 x-microsoft-antispam: BCL:0;ARA:14566002|461199028|41001999006|19110799006|15080799009|8060799009|8062599006|1602099012|102099032|440099028|4302099013|3412199025|10035399007; 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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: 7570987c-c0e0-4b12-73bd-08dda457d99e X-MS-Exchange-CrossTenant-originalarrivaltime: 05 Jun 2025 17:38:57.6155 (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: MN6PR02MB10728 X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: F055FC000A X-Stat-Signature: uzn3q1w96mo5i36zw8tyk4xit534bn35 X-Rspam-User: X-HE-Tag: 1749145140-279077 X-HE-Meta: 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 OOCwQT3i 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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: Thomas Zimmermann Sent: Thursday, June 5, 2025 = 8:36 AM >=20 > Hi >=20 > Am 04.06.25 um 23:43 schrieb Michael Kelley: > [...] > > Nonetheless, there's an underlying issue. A main cause of the differenc= e > > 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 tot= al of > > about 3,000,000 messages (~90K/second). That's a lot of additional load > > 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 th= e > > ring buffer for sending messages to the Hyper-V host gets full -- Hyper= -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 excessiv= ely > > 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. >=20 > I try to address the problem with the patches at >=20 > https://lore.kernel.org/dri-devel/20250605152637.98493-1-tzimmermann@suse= .de/ >=20 > Testing and feedback is much appreciated. >=20 Nice! I ran the same test case with your patches, and everything works well. The 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. Total 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 are small enough that the difference is in the noise. Question: what is the def= ault value for the simulated vblank rate? Just curious ... Michael