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Tue, 14 Jun 2022 15:58:31 +0000 (GMT) X-AuditID: cbfec36f-bfdff700000025aa-c6-62a8b0271081 Received: from SSI-EX4.ssi.samsung.com ( [105.128.2.145]) by ussmgxs3new.samsung.com (USCPEXMTA) with SMTP id AD.FC.52945.620B8A26; Tue, 14 Jun 2022 11:58:30 -0400 (EDT) Received: from SSI-EX3.ssi.samsung.com (105.128.2.228) by SSI-EX4.ssi.samsung.com (105.128.2.229) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id 15.1.2375.24; Tue, 14 Jun 2022 08:58:30 -0700 Received: from SSI-EX3.ssi.samsung.com ([105.128.5.228]) by SSI-EX3.ssi.samsung.com ([105.128.5.228]) with mapi id 15.01.2375.024; Tue, 14 Jun 2022 08:58:30 -0700 From: Vincent Fu To: "axboe@kernel.dk" , "fio@vger.kernel.org" CC: Vincent Fu Subject: [PATCH 3/5] HOWTO: improve description of latency measures Thread-Topic: [PATCH 3/5] HOWTO: improve description of latency measures Thread-Index: AQHYgAeXYkfonsLA+kyRzDi3vqgTAQ== Date: Tue, 14 Jun 2022 15:58:29 +0000 Message-ID: <20220614155822.307771-4-vincent.fu@samsung.com> In-Reply-To: <20220614155822.307771-1-vincent.fu@samsung.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [105.128.2.176] Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-CFilter-Loop: Reflected X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFvrOIsWRmVeSWpSXmKPExsWy7djX87rqG1YkGez/JWqx+m4/m8XHWS+Y HZg8Lp8t9fi8SS6AKYrLJiU1J7MstUjfLoEr40jnSeaC7xIVu6//ZW5gnCXUxcjJISFgIvH3 9G+2LkYuDiGBlYwSyyf0sUA4rUwSf9b1sMJU7fg+AapqLaPE/cV72CGcT4wSn+d8Y4ZwljFK XDxxASjDwcEmoCnxdn8BSLeIQJjEz0fbwSYxC6hLHNu4gQ3EFhZwlvj/rZEVosZDYuuRl0wQ tp7Eg1tTmUHGsAioSuzptAQJ8wrYSMy908MOYnMK2ErM2ToPrJxRQEzi+6k1TBDjxSVuPZnP BHG0oMSi2XuYIWwxiX+7HrJB2IoS97+/ZIeo15O4MXUKG4StLbFs4WtmiF2CEidnPmGBqJeU OLjiBjhUJAR6OSRevz0OtcBF4uvxTVBDpSWmr7kMVdTOKDF34xeo7gmMEtefSEHY1hL/Oq9B beaT+PvrEeMERuVZSA6fheSoWUiOmoXkqAWMLKsYxUuLi3PTU4uN8lLL9YoTc4tL89L1kvNz NzEC08bpf4fzdzBev/VR7xAjEwfjIUYJDmYlEd7JF5clCfGmJFZWpRblxxeV5qQWH2KU5mBR EuddlrkhUUggPbEkNTs1tSC1CCbLxMEp1cDkfvDLdw5x5eubQs1Ks9YVvDj1Q3LZ88ty9yyd OIqO5C5uXDfp1fnAK4+3RdSkMf22PGjpyLJVNuNoUtiaCNfJ60RvWWr0vrG20Gtbfpcjd+YB v2l68wuFq44qfPNOadQ9HV3bMj3m15Pvpfq1+asuPcqz+nt0Yuj8dN6tGkKrWqZ6HSs3akr8 aPuGdeKW4yk6p1skX1t/fx0x46my/V5t9m9iD+LCZ03a+fWJ0rwgi/ObUqpWzPfa2MHROzf/ 1ZRZnFzOR7LT/bWVrdgYl74Mczvr2iK3bo9dafGnFE3lc1p7fqrbB0/xuPDBynRCuehC9iw2 D9WGmp3cAs1/dTdJXmwKTk7eX3jB5v7Fn+pKLMUZiYZazEXFiQAXmVCtigMAAA== X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFmpnkeLIzCtJLcpLzFFi42LJbGCaqKu2YUWSwduJZhar7/azWXyc9YLZ gcnj8tlSj8+b5AKYorhsUlJzMstSi/TtErgyjnSeZC74LlGx+/pf5gbGWUJdjJwcEgImEju+ T2DrYuTiEBJYzShx/+4LKOcTo8S0Tb+ZIJxljBIP2pcwdzFycLAJaEq83V8A0i0iECbx89F2 VhCbWUBd4tjGDWwgtrCAs8T/b42sEDUeEluPvGSCsPUkHtyaCjaGRUBVYk+nJUiYV8BGYu6d HnYQWwjI3rXlCDOIzSlgKzFn6zywVkYBMYnvp9YwQawSl7j1ZD4TxAMCEkv2nGeGsEUlXj7+ xwphK0rc//6SHaJeT+LG1ClsELa2xLKFr5kh9gpKnJz5hAWiXlLi4IobLBMYxWchWTELSfss JO2zkLQvYGRZxSheWlycm15RbJyXWq5XnJhbXJqXrpecn7uJERhXp/8djtnBeO/WR71DjEwc jIcYJTiYlUR4J19cliTEm5JYWZValB9fVJqTWnyIUZqDRUmc1yN2YryQQHpiSWp2ampBahFM lomDU6qBSfv3twLZ3Kr/UYGaTy4e+pB5abXc0ZqVVhOObllw3l1uWUTDxFt1iVVJrtIW/K4f xfk2pAkwSXM9+DmTjXPq7/vrjd1mxr/mOZ6l+ev3jjcv592ruFQkZxKan6e+kneuYdWzLf6K 3vvmynv/nHRd8mHfg7cVVXe0Ky/p/ZQOcorOVwgRCrq46syZtZtsCliemG/Q3jn9obmNh/jd v0f97zztf3vcu6nk58x1yQe37L7H/OXE6t2ys6b6ZDvvTBJoPxjpPunr5Lcfz+w773V43j4b Ni1Ts+aMtxtDnhXeETxubmAe/eNx7JlyuQ2fJupcOxXcvqn82OOjTgoTdBwO5/LEHVnqe1f8 utes7W+jP9grsRRnJBpqMRcVJwIAxQnOyBoDAAA= X-CMS-MailID: 20220614155831uscas1p2312cb623924e5df60abefb210affa1f4 CMS-TYPE: 301P X-CMS-RootMailID: 20220614155831uscas1p2312cb623924e5df60abefb210affa1f4 References: <20220614155822.307771-1-vincent.fu@samsung.com> Precedence: bulk List-ID: X-Mailing-List: fio@vger.kernel.org - clarify how submission latency is calculated for async ioengines - it is slat (not clat) that is near zero for sync ioengines - Note that submission latency + completion latency =3D total latency Signed-off-by: Vincent Fu --- HOWTO.rst | 29 ++++++++++++++++++----------- 1 file changed, 18 insertions(+), 11 deletions(-) diff --git a/HOWTO.rst b/HOWTO.rst index 28ac2b7c..470777e2 100644 --- a/HOWTO.rst +++ b/HOWTO.rst @@ -4165,24 +4165,31 @@ writes in the example above). In the order listed,= they denote: **slat** Submission latency (**min** being the minimum, **max** being the maximum, **avg** being the average, **stdev** being the standard - deviation). This is the time it took to submit the I/O. For - sync I/O this row is not displayed as the slat is really the - completion latency (since queue/complete is one operation there). - This value can be in nanoseconds, microseconds or milliseconds --- - fio will choose the most appropriate base and print that (in the - example above nanoseconds was the best scale). Note: in :option:`--mini= mal` mode - latencies are always expressed in microseconds. + deviation). This is the time from when fio initialized th= e I/O + to submission. For synchronous ioengines this includes th= e time + up until just before the ioengine's queue function is call= ed. + For asynchronous ioengines this includes the time up throu= gh the + completion of the ioengine's queue function (and commit fu= nction + if it is defined). For sync I/O this row is not displayed = as the + slat is negligible. This value can be in nanoseconds, + microseconds or milliseconds --- fio will choose the most + appropriate base and print that (in the example above + nanoseconds was the best scale). Note: in :option:`--mini= mal` + mode latencies are always expressed in microseconds. =20 **clat** Completion latency. Same names as slat, this denotes the time from - submission to completion of the I/O pieces. For sync I/O, clat will - usually be equal (or very close) to 0, as the time from submit to - complete is basically just CPU time (I/O has already been done, see slat - explanation). + submission to completion of the I/O pieces. For sync I/O, = this + represents the time from when the I/O was submitted to the + operating system to when it was completed. For asynchronou= s + ioengines this is the time from when the ioengine's queue = (and + commit if available) functions were completed to when the = I/O's + completion was reaped by fio. =20 **lat** Total latency. Same names as slat and clat, this denotes the time from when fio created the I/O unit to completion of the I/O operation. + It is the sum of submission and completion latency. =20 **bw** Bandwidth statistics based on samples. Same names as the xlat stats, --=20 2.25.1