On Mon, Jun 25, 2012 at 12:24 AM, Shaohua Li <shli@xxxxxxxxxx> wrote: > Like raid 1/10, raid5 uses one thread to handle stripe. In a fast storage, the > thread becomes a bottleneck. raid5 can offload calculation like checksum to > async threads. And if storge is fast, scheduling async work and running async > work will introduce heavy lock contention of workqueue, which makes such > optimization useless. And calculation isn't the only bottleneck. For example, > in my test raid5 thread must handle > 450k requests per second. Just doing > dispatch and completion will make raid5 thread incapable. The only chance to > scale is using several threads to handle stripe. > > With this patch, user can create several extra threads to handle stripe. How > many threads are better depending on disk number, so the thread number can be > changed in userspace. By default, the thread number is 0, which means no extra > thread. > > In a 3-disk raid5 setup, 2 extra threads can provide 130% throughput > improvement (double stripe_cache_size) and the throughput is pretty close to > theory value. With >=4 disks, the improvement is even bigger, for example, can > improve 200% for 4-disk setup, but the throughput is far less than theory > value, which is caused by several factors like request queue lock contention, > cache issue, latency introduced by how a stripe is handled in different disks. > Those factors need further investigations. > > Signed-off-by: Shaohua Li <shli@xxxxxxxxxxxx> Can you share a bit more about your test setup? Is this single-threaded throughput? I'm wondering if we can take advantage of keeping the work cpu local. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
