Hi Jens I found out that when I remove BIO_RW_SYNCIO from dm-kcopyd.c, performance when writing to the snapshot origin is increased twice. In this workload, snapshot driver reads a lot of 8k chunks from one place on the disk and writes them to the other place on the same disk. Without BIO_RW_SYNCIO, it is twice faster with CFQ scheduler. What does BIO_RW_SYNCIO exactly do? Does it attempt to decrease latency and decrease throughput? (so that disk head seeks more between the source and destination and it causes performance degradation) Is there some general guidance, when use BIO_RW_SYNCIO and when not? Mikulas -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
