kkk 1024 cores i will mark this email and go back when i get one 1024cores cpu maybe just some 2 years? 10 years? 2012/6/28 NeilBrown <neilb@xxxxxxx> > > On Thu, 28 Jun 2012 20:29:21 -0500 Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx> > wrote: > > > 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. > > > > Not an easy question to answer. It just doesn't "taste" nice. > I certainly like the performance and if this is the only way to get that > performance then we'll probably go that way. But I'm not convinced it is the > only way and I want to explore other options first. > I guess it feels a bit heavy handed. On machines with 1024 cores, per-cpu > allocations and per-cpu threads are not as cheap as they are one 2-core > machines. And I'm hoping for a 1024-core phone soon :-) > > NeilBrown > -- Roberto Spadim Spadim Technology / SPAEmpresarial -- 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
