From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-189.mta1.migadu.com (out-189.mta1.migadu.com [95.215.58.189]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 14BD91547E2 for ; Thu, 19 Dec 2024 05:49:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.189 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734587357; cv=none; b=TU8Cmnn5ZmpprpVoUPH9oloCoi2HtxmJ5nwILYFo6oYh/++fblkOKl1DD9D60YZbj5KVb4OJ5KW2GNbnCCh4hXfzEgViONjVV2gKlhljXicoHYvPf9NdeOigHqJ604020beh2hAWNQ6nVd8L4vWBfkdDBhFltCk6Une7K6zCz1c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734587357; c=relaxed/simple; bh=3HBI5vOJhzDVa9C45kvTZsvkTt5M4M9NGjtPlj1opIw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Ma7WLXgRvMDcSHgGnlJDjul0ZOkvMk4eEDkhO+OmUatBk4GiLoKR9Lb+WpD4UxFkSI4vX6tF6sDpNpQ/AprLcSS01uI2+VFUfNiRsU5D4jzP9+3JCWSCv3T/XRkXOpspSClvnkZmSfjNTq+UurSYhzUH3WwkoKpUI0fWNAtO2nw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=gIIodoxh; arc=none smtp.client-ip=95.215.58.189 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="gIIodoxh" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1734587351; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=GxOTIHaIVBN6tNPdwHI5uDp585nGYq3Fwp1EQkg5m9o=; b=gIIodoxhI1wRl+rQP1JKZosWAhJFPBVGP9E38MoBTo75QYxxZHrZUkln+ubQe7b+L/d2US 4QK6hQaBFogZsS/h6ELnFw1sF5y2ahEmMrsMM8tyBYi5SVWY/1793IGuTpdFvzs8mPN92m e++f5weNhlcOALB/95I31v7+ahmWM6Y= Date: Thu, 19 Dec 2024 13:49:02 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v2] loongarch/mm: disable WUC for pgprot_writecombine as same as ioremap_wc To: Icenowy Zheng , Xi Ruoyao , WANG Xuerui , Huacai Chen Cc: Andrew Morton , "Mike Rapoport (IBM)" , Baoquan He , "Matthew Wilcox (Oracle)" , David Hildenbrand , Zhen Lei , Thomas Gleixner , Zhihong Dong , loongarch@lists.linux.dev, linux-kernel@vger.kernel.org References: <20231009042841.635366-1-uwu@icenowy.me> <4f1af31b-15be-cb47-6b34-45de1b5696be@loongson.cn> <42b0e6f6-c2b5-49c6-b1f2-0200bef913da@xen0n.name> <3641d3fe-c2e7-868f-ab0d-3951c9a78b6d@loongson.cn> <8373ccfd93b0402caf9f5c06a2d9b93b3c0d0b49.camel@xry111.site> <1e0f2174a72011cb1c78eeecbbf82a4ff108bf8a.camel@icenowy.me> <1090f735-8252-453f-b6c8-0ec35881ff32@linux.dev> <932a9a93c00082645df465862231f6d8c91f3bf6.camel@icenowy.me> <80e0813a-0651-41cf-a82d-776acbf1a5bc@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Sui Jingfeng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 2024/12/19 12:49, Icenowy Zheng wrote: > 在 2024-12-19星期四的 10:54 +0800，Sui Jingfeng写道： >> On 2024/12/18 20:43, Icenowy Zheng wrote: >>> For the fact of drm/ast's dramatical drop, it's because write to >>> the >>> framebuffer can no longer be reordered. >> >> No, your understanding is wrong, very very wrong and a big wrong. >> >> It's not because it can't reorder the write. Rather, it's because >> that the CPU can't do write gathering and can't do burst write any >> more. > Write gathering is a kind of write reordering, No, your understanding is broken. Write gathering *isn't* a kind of write reordering. Its doesn't have to reorder, it just cache the write operation with the CPU's write buffer. > comparing to strongly > ordered writing (which is literally one byte per write). > >> So do you still think your patch is harmless? > Well, I said that performance w/o correctness is meaningless. The point is that Write-Combine on drm/ast will get both correctness and performance. >> -- Best regards, Sui