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Tue, 17 Oct 2023 23:32:02 -0700 (PDT) MIME-Version: 1.0 References: <202310172247.b9959bd4-oliver.sang@intel.com> <2023101759-front-ember-6354@gregkh> In-Reply-To: <2023101759-front-ember-6354@gregkh> From: Max Kellermann Date: Wed, 18 Oct 2023 08:31:51 +0200 Message-ID: Subject: Re: [linux-next:master] [drivers/char/mem] 1b057bd800: stress-ng.splice.ops_per_sec -99.8% regression To: Greg Kroah-Hartman Cc: kernel test robot , oe-lkp@lists.linux.dev, lkp@intel.com, Linux Memory Management List , linux-kernel@vger.kernel.org, ying.huang@intel.com, feng.tang@intel.com, fengwei.yin@intel.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 5658340022 X-Rspam-User: X-Stat-Signature: xsr66s7eymbsar6mcnd9k8o53h81ep7c X-Rspamd-Server: rspam03 X-HE-Tag: 1697610724-631642 X-HE-Meta: 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 /Qwt4aav FOwExpEsXf3BT/KUIkImC8MsJ3VbyAEs9IEyY2lm+8YfBxZoePM82GiChEBA7l3/lBr3G6XCkWOYB1WU4U6LLPsQ22OfpzjzDr13Hp1GHmlzYLNU2OVmjSNFyTsCnn8ijmmRPBUHg0RvRLgUNeWLtFfpf9uIbj2wn3U394dQBSOcqiFB6tA3Qn14iw2ZBv0KHTthFHLpQhNyQU5qhALHdOINM5zgljZXYijSM+1uqD9XIi1cI1cDafKhyfqoVLhn/17ZAUlFDUxIib+Dg2rNsGcpqCbhjFWmQcr2q X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Oct 17, 2023 at 6:57=E2=80=AFPM Greg Kroah-Hartman wrote: > So everything now goes faster, right? -99.8% regression means 99.8% > faster? That's what I thought, too, and sounds reasonable considering this test is described as "stress copying of /dev/zero to /dev/null", but... it's not what that test actually does. Contrary to the description, it doesn't use /dev/zero at all, neither does it use /dev/full. So it shouldn't be affected by my patch at all. strace of that test's setup: pipe2([4, 5], 0) =3D 0 openat(AT_FDCWD, "/dev/null", O_WRONLY) =3D 6 Then it loops: vmsplice(5, [{iov_base=3D"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0= \0\0\0\0\0\0\0\0"..., iov_len=3D65536}], 1, 0) =3D 65536 splice(4, NULL, 6, NULL, 65536, SPLICE_F_MOVE) =3D 65536 write(5, "\334\360U\300~\361\20jV\367\263,\221\3724\332>7\31H2|\20\254\314= \212y\275\334I\304\207"..., 4096) =3D 4096 vmsplice(4, [{iov_base=3D"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0= \0\0\0\0\0\0\0\0"..., iov_len=3D4096}], 1, 0) =3D 4096 I don't get it.