On 7/14/19 11:45 PM, Zhengyuan Liu wrote: > > On 7/15/19 11:51 AM, Jens Axboe wrote: >> On Jul 14, 2019, at 9:38 PM, Zhengyuan Liu <liuzhengyuan@xxxxxxxxxx> wrote: >>> >>>> On 7/14/19 5:44 AM, Jens Axboe wrote: >>>>> On 7/12/19 10:54 PM, Zhengyuan Liu wrote: >>>>> As we introduced three lists(async, defer, link), there could been >>>>> many sqe allocation. A natural idea is using kmem_cache to satisfy >>>>> the allocation just like io_kiocb does. >>>> A change like this needs to come with some performance numbers >>>> or utilization numbers showing the benefit. I have considered >>>> doing this before, but just never got around to testing if it's >>>> worth while or not. >>>> Have you? >>> I only did some simple testing with fio. The benefit was deeply depend on the IO scenarios. For random and direct IO , it appears to be nearly no seq copying, but for buffered sequential rw, it appears to be more than 60% copying compared to original submition. >> Right, which is great as it’s then working as designed! But my >> question was, for that sequential case, what kind of speed up (or >> reduction in overhead) do you see from allocating the unit out of >> slab vs kmalloc? There has to be a win there for the change to be >> worthwhile. > > Thanks for your comments Jens. No speed up indeed in overhead from my > testing. Then I suggest we just drop this change, it only makes sense if there's a win. -- Jens Axboe
