From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f42.google.com (mail-wm1-f42.google.com [209.85.128.42]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 365593DF018 for ; Thu, 18 Jun 2026 09:59:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.42 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781776752; cv=none; b=fvJADY/dHVbbJnAIeALeRw64f5Qb0ZdcMo/MIPdAKQrNrex83htDm+rrLhgBIuwS+UO15l45OT2T65YjZ7nx3Y03gDQPbQXcpXPMIKmd7MbypIQiS54YMV0H6+1PN5pM9SQxDF3g+YbVC536L0v2Us8QOopyFjbk0FcBTxX2tkY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781776752; c=relaxed/simple; bh=gLUutZyLJxZbKf4agxXUs15ykDIeHM9nhDCepEXWEm4=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=SwVLIEaV7Z/jzDKqz3u0mpEUnU/zRm2ja8qw4CgNX5dtPI36V2i+IATodh0eqIK97sUpDxae+L+KAlPnt0vxzsAkJJ6K1hq+pQH48hPMBHjpRtbDSzu2bI5uchKbxgKP0wQelslPd+hEBrxBh5iIKJtWmqjT4idJXIeBOxq4FMU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=agOj3rAw; arc=none smtp.client-ip=209.85.128.42 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="agOj3rAw" Received: by mail-wm1-f42.google.com with SMTP id 5b1f17b1804b1-490cf322ed0so4632195e9.1 for ; Thu, 18 Jun 2026 02:59:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1781776749; x=1782381549; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:from:to:cc:subject:date :message-id:reply-to; bh=pzjkYvyfaRfjDGoow7iIRFvjI6CXIQdXmrKP5JQFJ6E=; b=agOj3rAwyegNduo1VaYdg8EgJ44RWLlQKOCEVJOTCvAFs3jXrg/M1h6r99k6MoUcyR xoye7KGNvhn14ZgS0VeU3cT59+3EiKH0Z2wynr8v4FCGY/hR0wDP1bH0TDjLQ90Q8F9Q i0Dd7ZXcTHiL3XxXdkmbWGHPfBZlUknAn//9lAieFu40t3EeCdCKB/jhbTUMG10MVdzr y8i12TNBH72nVrP7M+G1DCva0JBxzFlbdAQVOzKWEnJSZI1/EYs8vKLtpj7eWo//qNib xy8hjLToEknbmLYBpP/+1pJk/XuSsSZetQ955PhuyjZC8PYYaYqSpMzhNULDCMncdukx he4A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1781776749; x=1782381549; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=pzjkYvyfaRfjDGoow7iIRFvjI6CXIQdXmrKP5JQFJ6E=; b=nU1SD5Hl6U0kp0EOJzkCC7lxApxo9a7bfCBJllpwcERvBHDsxpFojnABjBmrhfMCI+ CUvYVdxm3gJ950hMkCZt1J7OKVcO1Zkzve3NV1rrLKS+dFYG5nDPDhUjb0rbwSZ6x1JY HhefMmXL88mn/ApIlB9FNZtvuVT4tACJeahlUB5qcrhhC1HhekMrKfPY7DK9vvSiHMUB 6U+HsUwrUaATsgloupUmIKax3yYZXq6CXF7BwFs+gNlAycCPIcK5+vUlYcNUqL4mC5Eq yy2UA+LRqblQJoeNgdsQJpksNqYo2e1h8OwrcurKpoXwrDMTkQIh6xsdUKkPShDfrX6e EkFw== X-Forwarded-Encrypted: i=1; AFNElJ8t187E8n/qhpTFCWYFXATxQtffNvkG4JGSmzhxzI67Nki/KVJaXs9Qrwpq6AkNyIJ85/BM6uyxEO75@vger.kernel.org X-Gm-Message-State: AOJu0YxXrPZL1y8JjNIW+G8PHyJzLS6YFbAXfYs9PvdBhTxISJEsnGjK oC+admQqTZL2tEbVUzsMr390H/Xw6/0uWm06A945yUhgfTXHgnk2UYFUqqVjdYeg X-Gm-Gg: AfdE7clHMR6vyxC12Ll9xFE3+kNHlvuYC4jMRhWrX5s5iqR70jVPF1fmfIE0rrx2sVY HYQzjBji+QxtgVJ8LsOVGnOdQSIKcDrJz9/3Bmx1wDRWNoPQ8jyukSxewx7aUzGG9VI9WxWUm7Y zXD49qZ/IwyNAb5YuksxOPQ4Xm1Xk8v0UO5ddmrPR7noj9NJmREF73xZrJ05Jk00sVEWthC/aYn 3C+cWAy+hbOwwMuiEv5aA1vBDP+11BlrO2iO+zhMQIaDtIq4YGIkaVj05anRNtMH5WVwAw+4QmB cU5BaI66mk/I05mq46mwptbI5RA3TpkCC1mGJqpSvi+KJj7WQpE5DSnH4/LkQZALo3PcdrCBRgM 6L8koXil/l62H93C6h0i2piQZxLMXQEAPiLnWCJwUjoallri38TvSIRX0HvoLFwiXkrROZsvPfN RMqfyLFQq+sfulWvve02qtce+QNRdQwHAPNlpvj4Ckhdt5b42oMA== X-Received: by 2002:a05:600c:4ed4:b0:492:1e36:85dd with SMTP id 5b1f17b1804b1-49238231011mr48552325e9.37.1781776749410; Thu, 18 Jun 2026 02:59:09 -0700 (PDT) Received: from pumpkin (82-69-66-36.dsl.in-addr.zen.co.uk. [82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4922fa96f0esm261148635e9.12.2026.06.18.02.59.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 18 Jun 2026 02:59:08 -0700 (PDT) Date: Thu, 18 Jun 2026 10:59:06 +0100 From: David Laight To: Christoph Hellwig Cc: Eric Biggers , Andrew Morton , linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, x86@kernel.org, linux-raid@vger.kernel.org Subject: Re: [PATCH v3] lib/raid/xor: x86: Add AVX-512 optimized xor_gen() Message-ID: <20260618105906.11033b70@pumpkin> In-Reply-To: <20260618092500.GC17530@lst.de> References: <20260615190338.26581-1-ebiggers@kernel.org> <20260617055653.GB19218@lst.de> <20260617110516.0a70950e@pumpkin> <20260618092500.GC17530@lst.de> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-raid@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 18 Jun 2026 11:25:00 +0200 Christoph Hellwig wrote: > On Wed, Jun 17, 2026 at 11:05:16AM +0100, David Laight wrote: > > > FYI, one or 2 sources are basically useless as they RAID5 configs > > > that have no benefits over simple mirroring and thus the numbers > > > aren't too interesting. > > > > With three disks you xor two buffers (src_count == 1) to get the parity > > to write to the third - so that is a valid RAID5 config. > > Sure. It did not say it is invalid, it just isn't very useful. > It gives you 2/3 the total capacity, mirroring only gives 1/2. But for a lot of uses I suspect disks are cheap enough that mirroring is usually the 'best bet'. It also means that there are a set of catastrophic failures that can be more easily recovered. It is probably more important to ensure all the disks in a raid set come from different production lines - otherwise they are likely to fail at the same time. At least modern disks don't (seem to) suffer from 'sticky oil' which would tend to stop them restarting after they got cold while turned off. Raid doesn't help when multiple disks fail to start! David