On Thu, May 19, 2016 at 7:15 PM, Joonsoo Kim <js1304@xxxxxxxxx> wrote: > 2016-05-20 5:20 GMT+09:00 Thomas Garnier <thgarnie@xxxxxxxxxx>: >> I ran the test given by Joonsoo and it gave me these minimum cycles >> per size across 20 usage: > > I can't understand what you did here. Maybe, it's due to my poor Engling. > Please explain more. You did single thread test? Why minimum cycles > rather than average? > I used your version of slab_test and ran it 20 times for each versions. I compared the minimum number of cycles as an optimal case for comparison. As you said slab_test results can be unreliable. Comparing the average across multiple runs always gave odd results. >> size,before,after >> 8,63.00,64.50 (102.38%) >> 16,64.50,65.00 (100.78%) >> 32,65.00,65.00 (100.00%) >> 64,66.00,65.00 (98.48%) >> 128,66.00,65.00 (98.48%) >> 256,64.00,64.00 (100.00%) >> 512,65.00,66.00 (101.54%) >> 1024,68.00,64.00 (94.12%) >> 2048,66.00,65.00 (98.48%) >> 4096,66.00,66.00 (100.00%) > > It looks like performance of all size classes are the same? > >> I assume the difference is bigger if you don't have RDRAND support. > > What does RDRAND means? Kconfig? How can I check if I have RDRAND? > Sorry, I was referring to the usage of get_random_bytes_arch which will be faster if the test machine support specific instructions (like RDRAND). >> Christoph, Joonsoo: Do you think it would be valuable to add a CONFIG >> to disable additional randomization per new page? It will remove >> additional entropy but increase performance for machines without arch >> specific randomization instructions. > > I don't think that it deserve another CONFIG. If performance is a matter, > I think that removing additional entropy is better until it is proved that > entropy is a problem. > I will do more testing before the next RFC to decide the best approach. > Thanks. Thanks for the comments, Thomas -- 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>