On Mon, Jun 1, 2020 at 7:02 AM Guoqing Jiang <guoqing.jiang@xxxxxxxxxxxxxxx> wrote: > > On 5/30/20 4:15 AM, Yufen Yu wrote: > > > > > > On 2020/5/29 20:22, Guoqing Jiang wrote: > >> On 5/29/20 1:49 PM, Yufen Yu wrote: > >>>> The 4k rand write performance drops from 100MB/S to 15MB/S?! How > >>>> about other > >>>> io sizes? Say 16k, 64K and 256K etc, it would be more convincing if > >>>> 64KB stripe > >>>> has better performance than 4KB stripe overall. > >>>> > >>> > >>> Maybe I have not explain clearly. Here, the fio test result shows > >>> that 4KB > >>> STRIPE_SIZE is not always have better performance. If applications > >>> request > >>> IO size mostly are bigger than 4KB, likely 1MB in test, set > >>> STRIPE_SIZE with > >>> a bigger value can get better performance. > >>> > >>> So, we try to provide a configurable STRIPE_SIZE, rather than fix > >>> STRIPE_SIZE as 4096. > >> > >> Which means if you set stripe size to 64KB then you should guarantee > >> the io size should > >> always bigger then 1MB, right? Given that, I don't think it makes > >> lots of sense. > >> > > > > No, I think you misunderstood. This patchset just want to optimize > > RAID5 performance > > for systems whose PAGE_SIZE is bigger than 4KB, likely 64KB on ARM64. > > Without this > > patchset, STRIPE_SIZE is equal to 64KB, means each IO size issued to > > array disk at > > least 64KB each time, Right? But filesystems usually issue bio in the > > unit of 4KB, > > means sometimes required 4KB but read or write 64KB on disk actually. > > That would > > waste resources. > > Yes,, it is hard for me to understand your way is better than just make > stripe size equals to > 4KB. > > > > > After this patchset, we set STRIPE_SIZE as default 4KB. For systems > > like X86, which > > just support 4KB PAGE_SIZE, it will not have any effect. But for 64KB > > arm64 system, > > it **normally** can get better performance on filesystems base on > > raid5, like dbench test. > > > > fio test just want to say that, we can also configure STRIPE_SIZE with > > a bigger value > > than default 4KB on 64KB ARM64 system when applications mostly issue > > big IO. It can > > get better performance for reducing IO split in RAID5. > > I do think the flexibility is not enough, if someone set stripe size to > 64KB by any chance, > people could complain the performance of raid5 really sucks if the io is > not big. And it is > not realistic to let people rebuild the module in case the io size is > changed, so it would be > more helpful if the stripe size can be changed dynamically without > recompile code. Agreed that it is not ideal to recompile the kernel/module to change stripe size. It is also possible that multiple arrays in one system have different optimal stripe sizes. I guess it shouldn't be too complicated to make this configurable per array? Thanks, Song
