Hello Willy, On Fri, Sep 22, 2017 at 08:11:22PM +0200, Willy Tarreau wrote: > On Fri, Sep 22, 2017 at 10:40:48AM -0700, Eduardo Valentin wrote: > > On Fri, Sep 22, 2017 at 07:31:45PM +0200, Greg KH wrote: > > > On Fri, Sep 22, 2017 at 10:16:06AM -0700, Eduardo Valentin wrote: > > > > Hello GregKH, > > > > > > > > I have been seeing several reports of performance issue with raid0 while performing fstrim on v4.9.y. > > > > Currently, if one performs: > > > > > > > > # fio --name fio_test_file --direct=1 --rw=randwrite --bs=4k --size=5G --numjobs=8 --group_reporting --directory=/mount/raid0 > > > > # rm -rf /media/nvme-raid0 > > > > # time fstrim -vvv -a > > > > real 3m41.102s > > > > user 0m0.000s > > > > sys 0m4.964s > > > > > > Also, is this a regression from older kernels? > > > > I personally did not try older than 4.9 kernels. but looking at git history, > > and the commit message of the fix, looks like this is long known issue that > > got fixed on v4.12. > > Or it may simply be something that couldn't be achieved without significantly > improving the underlying infrastructure using the patches you've spotted (and > possibly a few others that you didn't notice but are required for stability > or to avoid breaking other subsystems). > > While I use 4.9 on many of my machines, I'd rather favor maximal stability > over an optimization for some operations that don't appear *that* often. > That said if the relevant maintainers consider it safe to backport, I'll > certainly welcome some performance improvements on my machines, but that's > not what I'm primarily looking for in stable kernels. > > And if we start to backport performance improvements into LTS kernels, > what will encourage users to upgrade to the next LTS ? Yeah, I pondered for several days before opening up this backport request exactly because of your concerns above. But what made me to decide to share the backport for the community consideration is the way I see this. To me, this is *not only* a matter of performance boost, but also a real fix. Mainly because the systems with v4.9.y become unresponsive while performing fstrim because of kernel CPU consumption with the fstrim implementation in raid0. Meaning, depending on how this is deployed, how you use your fs, and how you deploy your raid, this can be a real problem on production systems. So, yeah, I hope you consider this not only from a performance perspective, but a fix for a real issue. > > Cheers, > Willy > -- All the best, Eduardo Valentin