From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 17DB7C433E2 for ; Tue, 19 May 2020 06:31:45 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id ED19E2070A for ; Tue, 19 May 2020 06:31:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org ED19E2070A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 831476E4F8; Tue, 19 May 2020 06:31:40 +0000 (UTC) Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by gabe.freedesktop.org (Postfix) with ESMTPS id DBD956E4EA for ; Tue, 19 May 2020 06:31:38 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id E0DEDAC64; Tue, 19 May 2020 06:31:39 +0000 (UTC) Subject: Re: [PATCH 1/2] drm/shmem: Use cached mappings by default To: Daniel Vetter , Gerd Hoffmann References: <20200513150312.21421-1-tzimmermann@suse.de> <20200513150312.21421-2-tzimmermann@suse.de> <20200514124050.GV206103@phenom.ffwll.local> <6cec8a8a-d642-cd93-906a-eafab49a12d7@suse.de> <20200515141044.GH206103@phenom.ffwll.local> <3e09cc7d-c609-e10a-3fe9-f40f3bbfaeaf@suse.de> <20200518082354.jeuyt7uzek73pjkp@sirius.home.kraxel.org> <3bc1a032-2e7a-d7a8-e5e6-8d53a9e9bd3a@suse.de> <20200518101132.ves2qswskaiajh2y@sirius.home.kraxel.org> <20200518144034.GN206103@phenom.ffwll.local> From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; keydata= mQENBFs50uABCADEHPidWt974CaxBVbrIBwqcq/WURinJ3+2WlIrKWspiP83vfZKaXhFYsdg XH47fDVbPPj+d6tQrw5lPQCyqjwrCPYnq3WlIBnGPJ4/jreTL6V+qfKRDlGLWFjZcsrPJGE0 BeB5BbqP5erN1qylK9i3gPoQjXGhpBpQYwRrEyQyjuvk+Ev0K1Jc5tVDeJAuau3TGNgah4Yc hdHm3bkPjz9EErV85RwvImQ1dptvx6s7xzwXTgGAsaYZsL8WCwDaTuqFa1d1jjlaxg6+tZsB 9GluwvIhSezPgnEmimZDkGnZRRSFiGP8yjqTjjWuf0bSj5rUnTGiyLyRZRNGcXmu6hjlABEB AAG0J1Rob21hcyBaaW1tZXJtYW5uIDx0emltbWVybWFubkBzdXNlLmRlPokBVAQTAQgAPhYh BHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJbOdLgAhsDBQkDwmcABQsJCAcCBhUKCQgLAgQWAgMB Ah4BAheAAAoJEGgNwR1TC3ojR80H/jH+vYavwQ+TvO8ksXL9JQWc3IFSiGpuSVXLCdg62AmR irxW+qCwNncNQyb9rd30gzdectSkPWL3KSqEResBe24IbA5/jSkPweJasgXtfhuyoeCJ6PXo clQQGKIoFIAEv1s8l0ggPZswvCinegl1diyJXUXmdEJRTWYAtxn/atut1o6Giv6D2qmYbXN7 mneMC5MzlLaJKUtoH7U/IjVw1sx2qtxAZGKVm4RZxPnMCp9E1MAr5t4dP5gJCIiqsdrVqI6i KupZstMxstPU//azmz7ZWWxT0JzgJqZSvPYx/SATeexTYBP47YFyri4jnsty2ErS91E6H8os Bv6pnSn7eAq5AQ0EWznS4AEIAMYmP4M/V+T5RY5at/g7rUdNsLhWv1APYrh9RQefODYHrNRH UE9eosYbT6XMryR9hT8XlGOYRwKWwiQBoWSDiTMo/Xi29jUnn4BXfI2px2DTXwc22LKtLAgT RjP+qbU63Y0xnQN29UGDbYgyyK51DW3H0If2a3JNsheAAK+Xc9baj0LGIc8T9uiEWHBnCH+R dhgATnWWGKdDegUR5BkDfDg5O/FISymJBHx2Dyoklv5g4BzkgqTqwmaYzsl8UxZKvbaxq0zb ehDda8lvhFXodNFMAgTLJlLuDYOGLK2AwbrS3Sp0AEbkpdJBb44qVlGm5bApZouHeJ/+n+7r 12+lqdsAEQEAAYkBPAQYAQgAJhYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJbOdLgAhsMBQkD wmcAAAoJEGgNwR1TC3ojpfcIAInwP5OlcEKokTnHCiDTz4Ony4GnHRP2fXATQZCKxmu4AJY2 h9ifw9Nf2TjCZ6AMvC3thAN0rFDj55N9l4s1CpaDo4J+0fkrHuyNacnT206CeJV1E7NYntxU n+LSiRrOdywn6erjxRi9EYTVLCHcDhBEjKmFZfg4AM4GZMWX1lg0+eHbd5oL1as28WvvI/uI aMyV8RbyXot1r/8QLlWldU3NrTF5p7TMU2y3ZH2mf5suSKHAMtbE4jKJ8ZHFOo3GhLgjVrBW HE9JXO08xKkgD+w6v83+nomsEuf6C6LYrqY/tsZvyEX6zN8CtirPdPWu/VXNRYAl/lat7lSI 3H26qrE= Message-ID: Date: Tue, 19 May 2020 08:31:32 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200518144034.GN206103@phenom.ffwll.local> X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: David Airlie , Sean Paul , Emil Velikov , dri-devel , Sam Ravnborg Content-Type: multipart/mixed; boundary="===============1253035350==" Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --===============1253035350== Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="AcXPGCKD0Zc0a5H3UuceDrmmELHniid5i" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --AcXPGCKD0Zc0a5H3UuceDrmmELHniid5i Content-Type: multipart/mixed; boundary="ih2KhEeQWgFsiS2dfJhHihtvfhkQDlFd0"; protected-headers="v1" From: Thomas Zimmermann To: Daniel Vetter , Gerd Hoffmann Cc: David Airlie , Emil Velikov , Sean Paul , dri-devel , Sam Ravnborg Message-ID: Subject: Re: [PATCH 1/2] drm/shmem: Use cached mappings by default References: <20200513150312.21421-1-tzimmermann@suse.de> <20200513150312.21421-2-tzimmermann@suse.de> <20200514124050.GV206103@phenom.ffwll.local> <6cec8a8a-d642-cd93-906a-eafab49a12d7@suse.de> <20200515141044.GH206103@phenom.ffwll.local> <3e09cc7d-c609-e10a-3fe9-f40f3bbfaeaf@suse.de> <20200518082354.jeuyt7uzek73pjkp@sirius.home.kraxel.org> <3bc1a032-2e7a-d7a8-e5e6-8d53a9e9bd3a@suse.de> <20200518101132.ves2qswskaiajh2y@sirius.home.kraxel.org> <20200518144034.GN206103@phenom.ffwll.local> In-Reply-To: <20200518144034.GN206103@phenom.ffwll.local> --ih2KhEeQWgFsiS2dfJhHihtvfhkQDlFd0 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable Hi Am 18.05.20 um 16:40 schrieb Daniel Vetter: > On Mon, May 18, 2020 at 12:11:32PM +0200, Gerd Hoffmann wrote: >> On Mon, May 18, 2020 at 10:50:15AM +0200, Thomas Zimmermann wrote: >>> Hi Gerd >>> >>> Am 18.05.20 um 10:23 schrieb Gerd Hoffmann: >>>>>> $ git grep drm_gem_shmem_mmap >>>>>> >>>>>> We also need correct access from userspace, otherwise the gpu is g= oing to >>>>>> be sad. >>>>> >>>>> I've been thinking about this, and I think it means that we can nev= er >>>>> have cached mappings anywhere. Even if shmem supports it internally= for >>>>> most drivers, as soon as the page are exported, the importer could >>>>> expect uncached memory. >>>> >>>> The importer should not expect anything but call dma-buf ops so the >>>> exporter has a chance to handle this correctly. >>> >>> I have the following case in mind: Suppose the exporter maps cached >>> pages and the importer expects uncached pages for DMA. There is >>> map_dma_buf/unmap_dma_buf, which can implement a cache flush for the >>> cached pages. Is it guaranteed that the importer calls this around ea= ch >>> DMA operation? >> >> I think the importer is supposed to do that, but I wouldn't surprised = if >> there are cases in tree where this isn't implemented correctly ... >=20 > Yup, this is very much a case of "supposed to" but "in practice, many > actually dont". The reason is that setting up mappings is expensive, so= > best avoid. Thanks to both of you for answering the question. >=20 > We filled that gap a few years after dma-buf landed with the > begin/end_cpu_access hooks, which allow the exporter to do cache flushi= ng > (using something like dma_sync_sg_for_device/cpu) and for this to all w= ork > properly. We even added ioctl so that the mmap on the dma-buf works > correctly. >=20 > But most importers still ignore this, so it's all fail :-/ But in theor= y > the pieces to make cached mappings work over dma-buf, even for importer= s > that need uncached, are all there. >=20 > Cheers, Daniel >=20 --=20 Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 N=C3=BCrnberg, Germany (HRB 36809, AG N=C3=BCrnberg) Gesch=C3=A4ftsf=C3=BChrer: Felix Imend=C3=B6rffer --ih2KhEeQWgFsiS2dfJhHihtvfhkQDlFd0-- --AcXPGCKD0Zc0a5H3UuceDrmmELHniid5i Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEchf7rIzpz2NEoWjlaA3BHVMLeiMFAl7DfUgACgkQaA3BHVML eiPXZAf/RJQmiV8mC8ptrzQ9Kty8TOCvB1RB012NT3W/jwDan0AzLDt4XUqgN4s0 FaCLEx7ijDbED7jxm7icuuC69O/m5Lw5pdDvx1SpHjTZ6258SJ89bJWVdYjSpSTw fduMdsfoOScxpVa9JSg8y1Lb70zNPznCuE0sdjnUvUOg1zi4tEdfCq/0shu6YKBE lG7+qihif4Pk8Bi6k4pcvFkOf5fbrbFmO4Q8up9p//VHE/LaXGFnrWjZEybQKOBm MLfwvEWTqGBWhIlVq8tyaBgyPYP2+e9SLPYrPzS3RY4NrNv217vwMZTMH8NQ5JQv bq0PEgKjS6ExK+bs3nKuWGz675ZXgg== =l7Bd -----END PGP SIGNATURE----- --AcXPGCKD0Zc0a5H3UuceDrmmELHniid5i-- --===============1253035350== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel --===============1253035350==--