disk because the potential risk could be that we should not be driving queue depth higher in presence of sync IO going to keep the max clat low. With some random and sequential reads going on in the system on one SATA disk I did not see any significant increase in max clat. So it looks like other WRITE queue depth control logic is doing its job. Here are the results. AVERAGE[brr, bsr, bufw together] [vanilla] ------- job Set NR ReadBW(KB/s) MaxClat(us) WriteBW(KB/s) MaxClat(us) --- --- -- ------------ ----------- ------------- ----------- brr 3 1 850 546345 0 0 bsr 3 1 14650 729543 0 0 bufw 3 1 0 0 23908 8274517 brr 3 2 981.333 579395 0 0 bsr 3 2 14149.7 1175689 0 0 bufw 3 2 0 0 21921 1.28108e+07 brr 3 4 898.333 1.75527e+06 0 0 bsr 3 4 12230.7 1.40072e+06 0 0 bufw 3 4 0 0 19722.3 2.4901e+07 brr 3 8 900 3160594 0 0 bsr 3 8 9282.33 1.91314e+06 0 0 bufw 3 8 0 0 18789.3 23890622 AVERAGE[brr, bsr, bufw mixed] [patched kernel] ------- job Set NR ReadBW(KB/s) MaxClat(us) WriteBW(KB/s) MaxClat(us) --- --- -- ------------ ----------- ------------- ----------- brr 3 1 837 417973 0 0 bsr 3 1 14357.7 591275 0 0 bufw 3 1 0 0 24869.7 8910662 brr 3 2 1038.33 543434 0 0 bsr 3 2 13351.3 1205858 0 0 bufw 3 2 0 0 18626.3 13280370 brr 3 4 913 1.86861e+06 0 0 bsr 3 4 12652.3 1430974 0 0 bufw 3 4 0 0 15343.3 2.81305e+07 brr 3 8 890 2.92695e+06 0 0 bsr 3 8 9635.33 1.90244e+06 0 0 bufw 3 8 0 0 17200.3 24424392 So looks like it might make sense to include this patch. Thanks Vivek Signed-off-by: Vivek Goyal Signed-off-by: Jens Axboe =ƚ