On 02/06/14 19:41, James Bottomley wrote: > On Thu, 2014-02-06 at 18:10 +0100, Bart Van Assche wrote: >> On 02/06/14 17:56, James Bottomley wrote: >>> Could you benchmark this lot and show what the actual improvement is >>> just for this series, if any? >> >> I see a performance improvement of 12% with the SRP protocol for the >> SCSI core optimizations alone (I am still busy measuring the impact of >> the blk-mq conversion but I can already see that it is really >> significant). Please note that the performance impact depends a lot on >> the workload (number of LUNs per SCSI host e.g.) so maybe the workload I >> chose is not doing justice to Christoph's work. And it's also important >> to mention that with the workload I ran I was saturating the target >> system CPU (a quad core Intel i5). In other words, results might be >> better with a more powerful target system. > > On what? Just the patches I indicated or the whole series? My specific > concern is that swapping a critical section for atomics may not buy us > anything even on x86 and may slow down non-x86. That's the bit I'd like > benchmarks to explore. The numbers I mentioned in my previous e-mail referred to the "SCSI data path micro-optimizations" patch series and the "A different approach for using blk-mq in the SCSI layer" series as a whole. I have run a new test in which I compared the performance between a kernel with these two patch series applied versus a kernel in which the four patches that convert host_busy, target_busy and device_busy into atomics have been reverted. For a workload with a single SCSI host, a single LUN, a block size of 512 bytes, the SRP protocol and a single CPU thread submitting I/O requests I see a performance improvement of 0.5% when using atomics. For a workload with a single SCSI host, eight LUNs and eight CPU threads submitting I/O I see a performance improvement of 3.8% when using atomics. Please note that these measurements have been run on a single socket system, that cache line misses are more expensive on NUMA systems and hence that the performance impact of these patches on a NUMA system will be more substantial. Bart. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
