On Mon, Oct 14, 2013 at 03:18:47PM -0700, Eric Dumazet wrote: > On Mon, 2013-10-14 at 14:19 -0700, Eric Dumazet wrote: > > On Mon, 2013-10-14 at 16:28 -0400, Neil Horman wrote: > > > > > So, early testing results today. I wrote a test module that, allocated a > > > 4k > > > buffer, initalized it with random data, and called csum_partial on it > > > 100000 > > > times, recording the time at the start and end of that loop. Results on > > > a 2.4 > > > GHz Intel Xeon processor: > > > > > > Without patch: Average execute time for csum_partial was 808 ns > > > With patch: Average execute time for csum_partial was 438 ns > > > > Impressive, but could you try again with data out of cache ? > > So I tried your patch on a GRE tunnel and got following results on a > single TCP flow. (short result : no visible difference) > >
So I went to reproduce these results, but was unable to (due to the fact that I only have a pretty jittery network to do testing accross at the moment with these devices). So instead I figured that I would go back to just doing measurements with the module that I cobbled together (operating under the assumption that it would give me accurate, relatively jitter free results (I've attached the module code for reference below). My results show slightly different behavior: Base results runs: 89417240 85170397 85208407 89422794 91645494 103655144 86063791 75647774 83502921 85847372 AVG = 875 ns Prefetch only runs: 70962849 77555099 81898170 68249290 72636538 83039294 78561494 83393369 85317556 79570951 AVG = 781 ns Parallel addition only runs: 42024233 44313064 48304416 64762297 42994259 41811628 55654282 64892958 55125582 42456403 AVG = 510 ns Both prefetch and parallel addition: 41329930 40689195 61106622 46332422 49398117 52525171 49517101 61311153 43691814 49043084 AVG = 494 ns For reference, each of the above large numbers is the number of nanoseconds taken to compute the checksum of a 4kb buffer 100000 times. To get my average results, I ran the test in a loop 10 times, averaged them, and divided by 100000. Based on these, prefetching is obviously a a good improvement, but not as good as parallel execution, and the winner by far is doing both. Thoughts? Neil #include <linux/module.h> #include <linux/kernel.h> #include <linux/netdevice.h> #include <linux/etherdevice.h> #include <linux/init.h> #include <linux/moduleparam.h> #include <linux/rtnetlink.h> #include <net/rtnetlink.h> #include <linux/u64_stats_sync.h> static char *buf; static int __init csum_init_module(void) { int i; __wsum sum = 0; struct timespec start, end; u64 time; buf = kmalloc(PAGE_SIZE, GFP_KERNEL); if (!buf) { printk(KERN_CRIT "UNABLE TO ALLOCATE A BUFFER OF %lu bytes\n", PAGE_SIZE); return -ENOMEM; } printk(KERN_CRIT "INITALIZING BUFFER\n"); get_random_bytes(buf, PAGE_SIZE); preempt_disable(); printk(KERN_CRIT "STARTING ITERATIONS\n"); getnstimeofday(&start); for(i=0;i<100000;i++) sum = csum_partial(buf, PAGE_SIZE, sum); getnstimeofday(&end); preempt_enable(); if (start.tv_nsec > end.tv_nsec) time = (ULLONG_MAX - end.tv_nsec) + start.tv_nsec; else time = end.tv_nsec - start.tv_nsec; printk(KERN_CRIT "COMPLETED 100000 iterations of csum in %llu nanosec\n", time); kfree(buf); return 0; } static void __exit csum_cleanup_module(void) { return; } module_init(csum_init_module); module_exit(csum_cleanup_module); MODULE_LICENSE("GPL"); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/