On Thu, 8 Dec 2016 09:18:06 +0000 Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote: > On Thu, Dec 08, 2016 at 09:22:31AM +0100, Jesper Dangaard Brouer wrote: > > On Wed, 7 Dec 2016 23:25:31 +0000 > > Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > On Wed, Dec 07, 2016 at 09:19:58PM +0000, Mel Gorman wrote: > > > > At small packet sizes on localhost, I see relatively low page allocator > > > > activity except during the socket setup and other unrelated activity > > > > (khugepaged, irqbalance, some btrfs stuff) which is curious as it's > > > > less clear why the performance was improved in that case. I considered > > > > the possibility that it was cache hotness of pages but that's not a > > > > good fit. If it was true then the first test would be slow and the rest > > > > relatively fast and I'm not seeing that. The other side-effect is that > > > > all the high-order pages that are allocated at the start are physically > > > > close together but that shouldn't have that big an impact. So for now, > > > > the gain is unexplained even though it happens consistently. > > > > > > > > > > Further investigation led me to conclude that the netperf automation on > > > my side had some methodology errors that could account for an artifically > > > low score in some cases. The netperf automation is years old and would > > > have been developed against a much older and smaller machine which may be > > > why I missed it until I went back looking at exactly what the automation > > > was doing. Minimally in a server/client test on remote maching there was > > > potentially higher packet loss than is acceptable. This would account why > > > some machines "benefitted" while others did not -- there would be boot to > > > boot variations that some machines happened to be "lucky". I believe I've > > > corrected the errors, discarded all the old data and scheduled a rest to > > > see what falls out. > > > > I guess you are talking about setting the netperf socket queue low > > (+256 bytes above msg size), that I pointed out in[1]. > > Primarily, yes. > > > From the same commit[2] I can see you explicitly set (local+remote): > > > > sysctl net.core.rmem_max=16777216 > > sysctl net.core.wmem_max=16777216 > > > > Yes, I set it for higher speed networks as a starting point to remind me > to examine rmem_default or socket configurations if any significant packet > loss is observed. > > > Eric do you have any advice on this setting? > > > > And later[4] you further increase this to 32MiB. Notice that the > > netperf UDP_STREAM test will still use the default value from: > > net.core.rmem_default = 212992. > > > > That's expected. In the initial sniff-test, I saw negligible packet loss. > I'm waiting to see what the full set of network tests look like before > doing any further adjustments. For netperf I will not recommend adjusting the global default /proc/sys/net/core/rmem_default as netperf have means of adjusting this value from the application (which were the options you setup too low and just removed). I think you should keep this as the default for now (unless Eric says something else), as this should cover most users. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>