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Received: from [127.0.0.2] (localhost [127.0.0.1]) by hr2.samba.org with esmtpsa (TLS1.3:ECDHE_SECP256R1__ECDSA_SECP256R1_SHA256__CHACHA20_POLY1305:256) (Exim) id 1tAU5V-00A3Hc-1B; Mon, 11 Nov 2024 13:04:13 +0000 Message-ID: Date: Mon, 11 Nov 2024 14:04:13 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 08/13] fs: add read support for RWF_UNCACHED To: Jens Axboe , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Cc: hannes@cmpxchg.org, clm@meta.com, linux-kernel@vger.kernel.org References: <20241108174505.1214230-1-axboe@kernel.dk> <20241108174505.1214230-9-axboe@kernel.dk> Content-Language: en-US, de-DE From: Stefan Metzmacher In-Reply-To: <20241108174505.1214230-9-axboe@kernel.dk> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Stat-Signature: xi4ngesge1jf6wgx936g84ois5oe8gyn X-Rspamd-Queue-Id: 5C4F04001F X-Rspam-User: X-HE-Tag: 1731330214-50764 X-HE-Meta: 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 0r2RxIHB x1Ip81v1xjL0tzTwcfzj2G5WLHQQ7Ru1SQu8AIknnmW7pLK7rM6UfQIk1lSvNdgrmG0HcdWDnKHJBPeT+fvo86nBb1m7CiFMUdslBh4bXvhiMKyfh09kqIr5JFCeZ7fMA1u2GIj9mhlHxFhYMN1JhGDgX4a0EmBv4v9OUNW9OFnyIyUuXMHLZhPdrTEvWFgBSUvQlR3HTasMtqyT3yecJFeFrid4v6L1ormfPcIeOAKautY9bEboJjUAi108qtddzX/kjJ8dgqonZEnjmLydLiuaiWAQtoarrReUfYf1SMXQ75k+C4EM39PcXE7ulV/oRqlZY X-Bogosity: Ham, tests=bogofilter, spamicity=0.000029, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Jens, > If the same test case is run with RWF_UNCACHED set for the buffered read, > the output looks as follows: > > Reading bs 65536, uncached 0 > 1s: 153144MB/sec > 2s: 156760MB/sec > 3s: 158110MB/sec > 4s: 158009MB/sec > 5s: 158043MB/sec > 6s: 157638MB/sec > 7s: 157999MB/sec > 8s: 158024MB/sec > 9s: 157764MB/sec > 10s: 157477MB/sec > 11s: 157417MB/sec > 12s: 157455MB/sec > 13s: 157233MB/sec > 14s: 156692MB/sec > > which is just chugging along at ~155GB/sec of read performance. Looking > at top, we see: > > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND > 7961 root 20 0 267004 0 0 S 3180 0.0 5:37.95 uncached > 8024 axboe 20 0 14292 4096 0 R 1.0 0.0 0:00.13 top > > where just the test app is using CPU, no reclaim is taking place outside > of the main thread. Not only is performance 65% better, it's also using > half the CPU to do it. Do you have numbers of similar code using O_DIRECT just to see the impact of the memcpy from the page cache to the userspace buffer... Thanks! metze