Hi, Jim, On Thu, Jun 9, 2011 at 7:49 PM, Jim Rees <rees@xxxxxxxxx> wrote: > Benny Halevy wrote: > > Â>> But note that this patch doesn't change anything unless you set the sysctl. > Â> there is a default value of 2M. maybe we can set it to page size by > Â> default so other layout are not affected and block layout can let > Â> users set it by hand if they care about performance. does this make > Â> sense? > > ÂIf doing it at all why use a sysctl rather than a mount option? > ÂOr maybe coding the logic for prefetching the layout iff sequential > Âaccess is detected is the right thing to do. > > I would rather see some automatic solution than to add either a sysctl or a > mount option. ÂFor now you can just drop that patch, as it's not needed for > basic pnfs block. The current code w/o the patch makes block layout performance very poor. Can we have it in for now, and when we have something smarter, change it back later? > > My understanding is that layoutget specifies a min and max, and the server > is returning the min. ÂTrond and Fred believe this should be fixed on the > server. ÂHere's the original report of the problem: > > From: Bergwolf > > From the network trace for pnfs, we can see the root cause for slow performance > is too many small layoutget. In specific, client asks for a layout of only 4K > pagesize (and server returns 8K due to block size alignment) at each time. > > The total IO time is 256/1.68 = 152 second. > There are 256*1024/8 = 32768 layoutget for the 256MB file. > On average, the time spent on each layoutget is 0.00456 second according to the > trace. > The total layoutget time is 32768* 0.00456 = 149 second, which takes up about > 98% of total IO time. > > So we should optimize layoutget's granularity to get better performance. For > instance, use a configurable prefetch size of 2MB or so. > -- Thanks, -Bergwolf -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
