Hi, Do you get the same effect when you don't set log_avg_msec? Do you know how far fio's timings are compared to blktrace? On 27 March 2017 at 15:36, Tarek <cashew250@xxxxxxxxx> wrote: > I don't have evidence to suggest that the min SLAT and CLAT are from > the same IO, speculation. Regardless, CLAT should not be 0 on any > device for a read. Nand read spec is 40uS. Flow is blkdiscard device, > precondition (seq fill twice, followed by 100GiB of random write), > then test. Any ideas? > > On Sat, Mar 25, 2017 at 3:29 AM, Sitsofe Wheeler <sitsofe@xxxxxxxxx> wrote: >> Hi, >> >> I don't know why the minimum clat is 0 usec (you might be able to >> investigate further by using blktrace on the device to see how much >> that disagrees with fio) but why do you believe that scenario happened >> on the exact same I/O(s) that had a 0 usec slat time? Do you have >> additional logs showing that was the case? >> >> On 24 March 2017 at 17:39, Tarek <cashew250@xxxxxxxxx> wrote: >>> Clat min is zero on a random read, how is that possible when NAND tR >>> spec is 20-60uS? Also isn't lat = slat + clat, 1 + 0 != 84 >>> >>> fio-2.15 >>> Starting 80 threads >>> >>> random-100r-0w_4k_qd1_jobs_16: (groupid=0, jobs=16): err= 0: >>> pid=22233: Tue Feb 21 15:41:33 2017 >>> Description : [Random R/W 100/0 QD1 BLK 4k Jobs 16] >>> read : io=1045.5GB, bw=609017KB/s, iops=152254, runt=1800001msec >>> slat (usec): min=1, max=6583, avg= 2.06, stdev= 1.01 >>> clat (usec): min=0, max=8728, avg=102.38, stdev=21.43 >>> lat (usec): min=84, max=8730, avg=104.52, stdev=21.45 >>> clat percentiles (usec): >>> | 1.00th=[ 85], 5.00th=[ 86], 10.00th=[ 87], 20.00th=[ 89], >>> | 30.00th=[ 91], 40.00th=[ 98], 50.00th=[ 101], 60.00th=[ 102], >>> | 70.00th=[ 104], 80.00th=[ 106], 90.00th=[ 116], 95.00th=[ 143], >>> | 99.00th=[ 175], 99.50th=[ 185], 99.90th=[ 225], 99.95th=[ 239], >>> | 99.99th=[ 270] >>> >>> >>> Fio Config: >>> thread >>> bs=4k >>> ioengine=libaio >>> direct=1 >>> buffered=0 >>> log_avg_msec=1000 >>> group_reporting=1 >>> rw=randread >>> numjobs=16 >>> iodepth=1 >>> time_based >>> runtime=1800 >>> refill_buffers >>> norandommap >>> filename=/dev/nvme0n1 >> >> -- >> Sitsofe | http://sucs.org/~sits/ -- Sitsofe | http://sucs.org/~sits/ -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
