Benny Halevy wrote: >> But note that this patch doesn't change anything unless you set the sysctl. > there is a default value of 2M. maybe we can set it to page size by > default so other layout are not affected and block layout can let > users set it by hand if they care about performance. does this make > sense? If doing it at all why use a sysctl rather than a mount option? Or maybe coding the logic for prefetching the layout iff sequential access 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. For now you can just drop that patch, as it's not needed for basic pnfs block. My understanding is that layoutget specifies a min and max, and the server is returning the min. Trond and Fred believe this should be fixed on the server. Here'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. -- 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
