On 6/28/2012 4:03 AM, NeilBrown wrote: > On Wed, 13 Jun 2012 17:11:43 +0800 Shaohua Li <shli@xxxxxxxxxx> wrote: > >> In raid1/10, all write requests are dispatched in a single thread. In fast >> storage, the thread is a bottleneck, because it dispatches request too slow. >> Also the thread migrates freely, which makes request completion cpu not match >> with submission cpu even driver/block layer has such capability. This will >> cause bad cache issue. Both these are not a big deal for slow storage. >> >> Switching the dispatching to percpu/perthread based dramatically increases >> performance. The more raid disk number is, the more performance boosts. In a >> 4-disk raid10 setup, this can double the throughput. >> >> percpu/perthread based dispatch doesn't harm slow storage. This is the way how >> raw device is accessed, and there is correct block plug set which can help do >> request merge and reduce lock contention. >> >> V2->V3: >> rebase to latest tree and fix cpuhotplug issue >> >> V1->V2: >> 1. droped direct dispatch patches. That has better performance imporvement, but >> is hopelessly made correct. >> 2. Add a MD specific workqueue to do percpu dispatch. > I still don't like the per-cpu allocations and the extra work queues. Why don't you like this method Neil? Complexity? The performance seems to be there. -- Stan -- 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
