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Tue, 2 Sep 2025 12:58:03 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id q23ILNvptmjRUQAAD6G6ig (envelope-from ); Tue, 02 Sep 2025 12:58:03 +0000 Message-ID: <5cd7f22d-e39a-4d37-8286-0194d6c9a818@suse.de> Date: Tue, 2 Sep 2025 14:58:03 +0200 Precedence: bulk X-Mailing-List: linux-hyperv@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 4/4] drm/hypervdrm: Use vblank timer To: Javier Martinez Canillas , louis.chauvet@bootlin.com, drawat.floss@gmail.com, hamohammed.sa@gmail.com, melissa.srw@gmail.com, mhklinux@outlook.com, simona@ffwll.ch, airlied@gmail.com, maarten.lankhorst@linux.intel.com Cc: dri-devel@lists.freedesktop.org, linux-hyperv@vger.kernel.org References: <20250901111241.233875-1-tzimmermann@suse.de> <20250901111241.233875-5-tzimmermann@suse.de> <87a53dfe87.fsf@minerva.mail-host-address-is-not-set> Content-Language: en-US From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spamd-Result: default: False [-2.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; FREEMAIL_TO(0.00)[redhat.com,bootlin.com,gmail.com,outlook.com,ffwll.ch,linux.intel.com]; TAGGED_RCPT(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; RCPT_COUNT_SEVEN(0.00)[11]; MIME_TRACE(0.00)[0:+]; MID_RHS_MATCH_FROM(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com,outlook.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_TLS_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; URIBL_BLOCKED(0.00)[suse.de:mid,suse.de:email,imap1.dmz-prg2.suse.org:helo]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.de:mid,suse.de:email] X-Spam-Flag: NO X-Spam-Level: X-Spam-Score: -2.80 Hi Am 02.09.25 um 10:30 schrieb Javier Martinez Canillas: > Thomas Zimmermann writes: > >> HyperV's virtual hardware does not provide vblank interrupts. Use a >> vblank timer to simulate the interrupt. Rate-limits the display's >> update frequency to the display-mode settings. Avoids excessive CPU >> overhead with compositors that do not rate-limit their output. >> >> Signed-off-by: Thomas Zimmermann >> --- > Reviewed-by: Javier Martinez Canillas > > [...] > >> >> @@ -111,11 +113,15 @@ static void hyperv_crtc_helper_atomic_enable(struct drm_crtc *crtc, >> crtc_state->mode.hdisplay, >> crtc_state->mode.vdisplay, >> plane_state->fb->pitches[0]); >> + >> + drm_crtc_vblank_on(crtc); >> } >> >> static const struct drm_crtc_helper_funcs hyperv_crtc_helper_funcs = { >> .atomic_check = drm_crtc_helper_atomic_check, >> + .atomic_flush = drm_crtc_vblank_atomic_flush, >> .atomic_enable = hyperv_crtc_helper_atomic_enable, >> + .atomic_disable = drm_crtc_vblank_atomic_disable, >> }; >> > I think your patch is correct due the driver not having an .atomic_disable > callback. But looking at the driver, I see that its .atomic_enable does: > > static void hyperv_crtc_helper_atomic_enable(struct drm_crtc *crtc, > struct drm_atomic_state *state) > { > ... > hyperv_update_situation(hv->hdev, 1, hv->screen_depth, > crtc_state->mode.hdisplay, > crtc_state->mode.vdisplay, > plane_state->fb->pitches[0]); > } > > and this function in turn does: > > int hyperv_update_situation(struct hv_device *hdev, u8 active, u32 bpp, > u32 w, u32 h, u32 pitch) > { > ... > msg.situ.video_output[0].active = active; > ... > } > > So I wonder if it should instead have a custom .atomic_disable that calls: > > hyperv_update_situation(hv->hdev, 0, hv->screen_depth, > crtc_state->mode.hdisplay, > crtc_state->mode.vdisplay, > plane_state->fb->pitches[0]); > > I'm not familiar with hyperv to know whether is a problem or not for the > host to not be notified that the guest display is disabled. But I thought > that should raise this question for the folks familiar with it. The feedback I got at https://lore.kernel.org/dri-devel/SN6PR02MB4157F630284939E084486AFED46FA@SN6PR02MB4157.namprd02.prod.outlook.com/ is that the vblank timer solves the problem of excessive CPU consumption on hypervdrm. Ans that's also the observation I had with other drivers. I guess, telling the host about the disabled display would still make sense. Best regards Thomas > -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstrasse 146, 90461 Nuernberg, Germany GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman HRB 36809 (AG Nuernberg)