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=-4.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 5D436C433E0 for ; Mon, 15 Feb 2021 14:55:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2FB2E64E34 for ; Mon, 15 Feb 2021 14:55:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230030AbhBOOze (ORCPT ); Mon, 15 Feb 2021 09:55:34 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59178 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229970AbhBOOz0 (ORCPT ); Mon, 15 Feb 2021 09:55:26 -0500 Received: from mail-ej1-x62a.google.com (mail-ej1-x62a.google.com [IPv6:2a00:1450:4864:20::62a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D8028C061756; Mon, 15 Feb 2021 06:54:45 -0800 (PST) Received: by mail-ej1-x62a.google.com with SMTP id jj19so11615180ejc.4; Mon, 15 Feb 2021 06:54:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-transfer-encoding:content-language; bh=vVdEfWSlmLCjTZzZsqvvIxgWNNo8H9xjhu0/9T9YVpU=; b=XlIog/eMeAk3If6nDNMJc83j9eaD9nfSoxl0yxZ4R4Xq3lypZ8xHagLCcVTP7/DuRo rl65fgWOqlyAcRN9WjoOI3SNfk1bKQSD64aK5ernmrZdVqDxF6yfj2B6mkbbkEfys+QJ fx6ngTmXggNrbsiBUHyK/Zq2I6yGWzajmCtxhCV5K3WibSWKws1CHCc4onZBYLnxDiyA nv48s2MBsHnGyYZUblPQwk9KTsfRQxXLB8P1z74f+PYG5A5MCPbdKJXu8JPBa6tbBBAC 7wvyRyuLf6nVbeuWvHapgwZsCvNyWzdxEkKK7Q459rL2C/5lS31JL+CBBLaZneUTEWid DafA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :content-language; bh=vVdEfWSlmLCjTZzZsqvvIxgWNNo8H9xjhu0/9T9YVpU=; b=o4wJKnsT/CpQ/DwSIDET5DkXq1wZSgtMmhj5O5K0eagMlhDgJMaCg2G3ePsdjaEOWj lU0yBEZF/NeHKG9ZBJghPpYLwsB4agVKlmewOVD2AOpZ0J2DnJdEdQ/mNI7/PC9iLsUa 2KDkJBCrBiVv2LOFd4/R6RVZJrsFMBIEdawrIiX0vHkBWTOz/yRG6qNrZ3BspiIqdCOe WSgBOCCmIIjWd615AlS0WMknLhwwCrOrNnvGLyZgrrVShjYvuoy0v06QfeRjCqM6/kZk +3qUtmavTmtIRRI8atMzy34EoyvrSk07Yah1l5skDR+Np+KvQrAvJV5+1a+QhkuQNYAp CL0Q== X-Gm-Message-State: AOAM533R1gx9VD0HTV9BWhMeghQp84BKFfEW1f0ZpJtoG3YNaKapsHcy GVU7gBnucUw0xVACZta9uek= X-Google-Smtp-Source: ABdhPJyKyQ+rcI1yMgx5DeqIr7yds4RFmEThUICE4kKcuA/yo4/N31AymywJRuTF1ELr74NJdEQU1w== X-Received: by 2002:a17:906:3412:: with SMTP id c18mr2583106ejb.146.1613400884593; Mon, 15 Feb 2021 06:54:44 -0800 (PST) Received: from ?IPv6:2a02:908:1252:fb60:83c6:b72d:87bd:4259? ([2a02:908:1252:fb60:83c6:b72d:87bd:4259]) by smtp.gmail.com with ESMTPSA id q20sm10743492ejs.17.2021.02.15.06.54.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 15 Feb 2021 06:54:44 -0800 (PST) Subject: Re: [Linaro-mm-sig] DMA-buf and uncached system memory To: David Laight , =?UTF-8?B?J0NocmlzdGlhbiBLw7ZuaWcn?= , Lucas Stach , Simon Ser Cc: "linaro-mm-sig@lists.linaro.org" , linux-media , lkml , dri-devel , "Sharma, Shashank" References: <91ff0bbb-ea3a-2663-3453-dea96ccd6dd8@amd.com> <8d23f1ca6fe76d8971365bf54ca71ba71698980d.camel@pengutronix.de> <7ecf008d-a1f5-ddff-c8ac-8e7bfaf9c680@amd.com> From: =?UTF-8?Q?Christian_K=c3=b6nig?= Message-ID: <33ffa837-a88a-db1c-7861-c70d67557665@gmail.com> Date: Mon, 15 Feb 2021 15:54:43 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am 15.02.21 um 15:41 schrieb David Laight: > From: Christian König >> Sent: 15 February 2021 12:05 > ... >> Snooping the CPU caches introduces some extra latency, so what can >> happen is that the response to the PCIe read comes to late for the >> scanout. The result is an underflow and flickering whenever something is >> in the cache which needs to be flushed first. > Aren't you going to get the same problem if any other endpoints are > doing memory reads? The PCIe device in this case is part of the SoC, so we have a high priority channel to memory. Because of this the hardware designer assumed they have a guaranteed memory latency. > Possibly even ones that don't require a cache snoop and flush. > > What about just the cpu doing a real memory transfer? > > Or a combination of the two above happening just before your request. > > If you don't have a big enough fifo you'll lose. > > I did 'fix' a similar(ish) issue with video DMA latency on an embedded > system based the on SA1100/SA1101 by significantly reducing the clock > to the VGA panel whenever the cpu was doing 'slow io'. > (Interleaving an uncached cpu DRAM write between the slow io cycles > also fixed it.) > But the video was the only DMA device and that was an embedded system. > Given the application note about video latency didn't mention what was > actually happening, I'm not sure how many people actually got it working! Yeah, I'm also not sure if AMD doesn't solve this with deeper fifos or more prefetching in future designs. But you gave me at least one example where somebody had similar problems. Thanks for the feedback, Christian. > > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales) > _______________________________________________ > Linaro-mm-sig mailing list > Linaro-mm-sig@lists.linaro.org > https://lists.linaro.org/mailman/listinfo/linaro-mm-sig 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=-2.0 required=3.0 tests=BAYES_00,DKIM_ADSP_CUSTOM_MED, DKIM_INVALID,DKIM_SIGNED,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 6AE80C433E0 for ; Mon, 15 Feb 2021 14:54:47 +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 087C964DF4 for ; Mon, 15 Feb 2021 14:54:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 087C964DF4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com 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 647846E8BF; Mon, 15 Feb 2021 14:54:46 +0000 (UTC) Received: from mail-ej1-x632.google.com (mail-ej1-x632.google.com [IPv6:2a00:1450:4864:20::632]) by gabe.freedesktop.org (Postfix) with ESMTPS id D99866E8BF for ; Mon, 15 Feb 2021 14:54:45 +0000 (UTC) Received: by mail-ej1-x632.google.com with SMTP id jt13so11645470ejb.0 for ; Mon, 15 Feb 2021 06:54:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-transfer-encoding:content-language; bh=vVdEfWSlmLCjTZzZsqvvIxgWNNo8H9xjhu0/9T9YVpU=; b=XlIog/eMeAk3If6nDNMJc83j9eaD9nfSoxl0yxZ4R4Xq3lypZ8xHagLCcVTP7/DuRo rl65fgWOqlyAcRN9WjoOI3SNfk1bKQSD64aK5ernmrZdVqDxF6yfj2B6mkbbkEfys+QJ fx6ngTmXggNrbsiBUHyK/Zq2I6yGWzajmCtxhCV5K3WibSWKws1CHCc4onZBYLnxDiyA nv48s2MBsHnGyYZUblPQwk9KTsfRQxXLB8P1z74f+PYG5A5MCPbdKJXu8JPBa6tbBBAC 7wvyRyuLf6nVbeuWvHapgwZsCvNyWzdxEkKK7Q459rL2C/5lS31JL+CBBLaZneUTEWid DafA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :content-language; bh=vVdEfWSlmLCjTZzZsqvvIxgWNNo8H9xjhu0/9T9YVpU=; b=YPKjQ99zGimI2j3Ul8k81FShlLzlgklXrIS8jcEfxO7CN98wC9vN+lMO8mV9Snsc2l qXljN+ru2Jc6EyRC55jkb4xeeRTlOoEehUgeIqcFJyXDvifrmapsqZwAXhX3r5fYznls Wz7Bi4+9pHm+qyIfebOxFNP5FKlMVfGnPzwalh7Bm5hxz9pP9CBnr9ks0pQICcn+b/kh sG0/ILAwmG8yxxC1fzRDfNGuZVDDm2HNeCt8YBvfKVg2mWA4Ni50hgPoX8agjEKJNvRz aWNsGpxOz5xtfB2eaj9DvMMDqbCRGWVKAOf2587k71YrndDJ+kYXveoL+6KGwdfmRt2K TIdQ== X-Gm-Message-State: AOAM530gotoTIKUuqhnBW/vYkx1UsMFpLzZvrywQ77zPvD9+IgE4rpR/ DfdYqAOeUIYy0kmFMli7HLeKH/1UTRgKQw== X-Google-Smtp-Source: ABdhPJyKyQ+rcI1yMgx5DeqIr7yds4RFmEThUICE4kKcuA/yo4/N31AymywJRuTF1ELr74NJdEQU1w== X-Received: by 2002:a17:906:3412:: with SMTP id c18mr2583106ejb.146.1613400884593; Mon, 15 Feb 2021 06:54:44 -0800 (PST) Received: from ?IPv6:2a02:908:1252:fb60:83c6:b72d:87bd:4259? ([2a02:908:1252:fb60:83c6:b72d:87bd:4259]) by smtp.gmail.com with ESMTPSA id q20sm10743492ejs.17.2021.02.15.06.54.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 15 Feb 2021 06:54:44 -0800 (PST) Subject: Re: [Linaro-mm-sig] DMA-buf and uncached system memory To: David Laight , =?UTF-8?B?J0NocmlzdGlhbiBLw7ZuaWcn?= , Lucas Stach , Simon Ser References: <91ff0bbb-ea3a-2663-3453-dea96ccd6dd8@amd.com> <8d23f1ca6fe76d8971365bf54ca71ba71698980d.camel@pengutronix.de> <7ecf008d-a1f5-ddff-c8ac-8e7bfaf9c680@amd.com> From: =?UTF-8?Q?Christian_K=c3=b6nig?= Message-ID: <33ffa837-a88a-db1c-7861-c70d67557665@gmail.com> Date: Mon, 15 Feb 2021 15:54:43 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US 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: "linaro-mm-sig@lists.linaro.org" , "Sharma, Shashank" , lkml , dri-devel , linux-media Content-Transfer-Encoding: base64 Content-Type: text/plain; charset="utf-8"; Format="flowed" Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" CgpBbSAxNS4wMi4yMSB1bSAxNTo0MSBzY2hyaWViIERhdmlkIExhaWdodDoKPiBGcm9tOiBDaHJp c3RpYW4gS8O2bmlnCj4+IFNlbnQ6IDE1IEZlYnJ1YXJ5IDIwMjEgMTI6MDUKPiAuLi4KPj4gU25v b3BpbmcgdGhlIENQVSBjYWNoZXMgaW50cm9kdWNlcyBzb21lIGV4dHJhIGxhdGVuY3ksIHNvIHdo YXQgY2FuCj4+IGhhcHBlbiBpcyB0aGF0IHRoZSByZXNwb25zZSB0byB0aGUgUENJZSByZWFkIGNv bWVzIHRvIGxhdGUgZm9yIHRoZQo+PiBzY2Fub3V0LiBUaGUgcmVzdWx0IGlzIGFuIHVuZGVyZmxv dyBhbmQgZmxpY2tlcmluZyB3aGVuZXZlciBzb21ldGhpbmcgaXMKPj4gaW4gdGhlIGNhY2hlIHdo aWNoIG5lZWRzIHRvIGJlIGZsdXNoZWQgZmlyc3QuCj4gQXJlbid0IHlvdSBnb2luZyB0byBnZXQg dGhlIHNhbWUgcHJvYmxlbSBpZiBhbnkgb3RoZXIgZW5kcG9pbnRzIGFyZQo+IGRvaW5nIG1lbW9y eSByZWFkcz8KClRoZSBQQ0llIGRldmljZSBpbiB0aGlzIGNhc2UgaXMgcGFydCBvZiB0aGUgU29D LCBzbyB3ZSBoYXZlIGEgaGlnaCAKcHJpb3JpdHkgY2hhbm5lbCB0byBtZW1vcnkuCgpCZWNhdXNl IG9mIHRoaXMgdGhlIGhhcmR3YXJlIGRlc2lnbmVyIGFzc3VtZWQgdGhleSBoYXZlIGEgZ3VhcmFu dGVlZCAKbWVtb3J5IGxhdGVuY3kuCgo+IFBvc3NpYmx5IGV2ZW4gb25lcyB0aGF0IGRvbid0IHJl cXVpcmUgYSBjYWNoZSBzbm9vcCBhbmQgZmx1c2guCj4KPiBXaGF0IGFib3V0IGp1c3QgdGhlIGNw dSBkb2luZyBhIHJlYWwgbWVtb3J5IHRyYW5zZmVyPwo+Cj4gT3IgYSBjb21iaW5hdGlvbiBvZiB0 aGUgdHdvIGFib3ZlIGhhcHBlbmluZyBqdXN0IGJlZm9yZSB5b3VyIHJlcXVlc3QuCj4KPiBJZiB5 b3UgZG9uJ3QgaGF2ZSBhIGJpZyBlbm91Z2ggZmlmbyB5b3UnbGwgbG9zZS4KPgo+IEkgZGlkICdm aXgnIGEgc2ltaWxhcihpc2gpIGlzc3VlIHdpdGggdmlkZW8gRE1BIGxhdGVuY3kgb24gYW4gZW1i ZWRkZWQKPiBzeXN0ZW0gYmFzZWQgdGhlIG9uIFNBMTEwMC9TQTExMDEgYnkgc2lnbmlmaWNhbnRs eSByZWR1Y2luZyB0aGUgY2xvY2sKPiB0byB0aGUgVkdBIHBhbmVsIHdoZW5ldmVyIHRoZSBjcHUg d2FzIGRvaW5nICdzbG93IGlvJy4KPiAoSW50ZXJsZWF2aW5nIGFuIHVuY2FjaGVkIGNwdSBEUkFN IHdyaXRlIGJldHdlZW4gdGhlIHNsb3cgaW8gY3ljbGVzCj4gYWxzbyBmaXhlZCBpdC4pCj4gQnV0 IHRoZSB2aWRlbyB3YXMgdGhlIG9ubHkgRE1BIGRldmljZSBhbmQgdGhhdCB3YXMgYW4gZW1iZWRk ZWQgc3lzdGVtLgo+IEdpdmVuIHRoZSBhcHBsaWNhdGlvbiBub3RlIGFib3V0IHZpZGVvIGxhdGVu Y3kgZGlkbid0IG1lbnRpb24gd2hhdCB3YXMKPiBhY3R1YWxseSBoYXBwZW5pbmcsIEknbSBub3Qg c3VyZSBob3cgbWFueSBwZW9wbGUgYWN0dWFsbHkgZ290IGl0IHdvcmtpbmchCgpZZWFoLCBJJ20g YWxzbyBub3Qgc3VyZSBpZiBBTUQgZG9lc24ndCBzb2x2ZSB0aGlzIHdpdGggZGVlcGVyIGZpZm9z IG9yIAptb3JlIHByZWZldGNoaW5nIGluIGZ1dHVyZSBkZXNpZ25zLgoKQnV0IHlvdSBnYXZlIG1l IGF0IGxlYXN0IG9uZSBleGFtcGxlIHdoZXJlIHNvbWVib2R5IGhhZCBzaW1pbGFyIHByb2JsZW1z LgoKVGhhbmtzIGZvciB0aGUgZmVlZGJhY2ssCkNocmlzdGlhbi4KCj4KPiAJRGF2aWQKPgo+IC0K PiBSZWdpc3RlcmVkIEFkZHJlc3MgTGFrZXNpZGUsIEJyYW1sZXkgUm9hZCwgTW91bnQgRmFybSwg TWlsdG9uIEtleW5lcywgTUsxIDFQVCwgVUsKPiBSZWdpc3RyYXRpb24gTm86IDEzOTczODYgKFdh bGVzKQo+IF9fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fCj4g TGluYXJvLW1tLXNpZyBtYWlsaW5nIGxpc3QKPiBMaW5hcm8tbW0tc2lnQGxpc3RzLmxpbmFyby5v cmcKPiBodHRwczovL2xpc3RzLmxpbmFyby5vcmcvbWFpbG1hbi9saXN0aW5mby9saW5hcm8tbW0t c2lnCgpfX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fXwpkcmkt ZGV2ZWwgbWFpbGluZyBsaXN0CmRyaS1kZXZlbEBsaXN0cy5mcmVlZGVza3RvcC5vcmcKaHR0cHM6 Ly9saXN0cy5mcmVlZGVza3RvcC5vcmcvbWFpbG1hbi9saXN0aW5mby9kcmktZGV2ZWwK