On Fri, 2009-01-23 at 10:06 +0200, Pekka Enberg wrote: > On Fri, 2009-01-23 at 08:52 +0200, Pekka Enberg wrote: > > > 1) If I start CPU_NUM clients and servers, SLUB's result is about 2% better than SLQB's; > > > 2) If I start 1 clinet and 1 server, and bind them to different physical cpu, SLQB's result > > > is about 10% better than SLUB's. > > > > > > I don't know why there is still 10% difference with item 2). Maybe cachemiss causes it? > > > > Maybe we can use the perfstat and/or kerneltop utilities of the new perf > > counters patch to diagnose this: > > > > http://lkml.org/lkml/2009/1/21/273 > > > > And do oprofile, of course. Thanks! > > I assume binding the client and the server to different physical CPUs > also means that the SKB is always allocated on CPU 1 and freed on CPU > 2? If so, we will be taking the __slab_free() slow path all the time on > kfree() which will cause cache effects, no doubt. > > But there's another potential performance hit we're taking because the > object size of the cache is so big. As allocations from CPU 1 keep > coming in, we need to allocate new pages and unfreeze the per-cpu page. > That in turn causes __slab_free() to be more eager to discard the slab > (see the PageSlubFrozen check there). > > So before going for cache profiling, I'd really like to see an oprofile > report. I suspect we're still going to see much more page allocator > activity Theoretically, it should, but oprofile doesn't show that. > there than with SLAB or SLQB which is why we're still behaving > so badly here. oprofile output with 2.6.29-rc2-slubrevertlarge: CPU: Core 2, speed 2666.71 MHz (estimated) Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (Unhalted core cycles) count 100000 samples % app name symbol name 132779 32.9951 vmlinux copy_user_generic_string 25334 6.2954 vmlinux schedule 21032 5.2264 vmlinux tg_shares_up 17175 4.2679 vmlinux __skb_recv_datagram 9091 2.2591 vmlinux sock_def_readable 8934 2.2201 vmlinux mwait_idle 8796 2.1858 vmlinux try_to_wake_up 6940 1.7246 vmlinux __slab_free #slaninfo -AD Name Objects Alloc Free %Fast :0000256 1643 5215544 5214027 94 0 kmalloc-8192 28 5189576 5189560 0 0 :0000168 2631 141466 138976 92 28 :0004096 1452 88697 87269 99 96 :0000192 3402 63050 59732 89 11 :0000064 6265 46611 40721 98 82 :0000128 1895 30429 28654 93 32 oprofile output with kernel 2.6.29-rc2-slqb0121: CPU: Core 2, speed 2666.76 MHz (estimated) Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (Unhalted core cycles) count 100000 samples % image name app name symbol name 114793 28.7163 vmlinux vmlinux copy_user_generic_string 27880 6.9744 vmlinux vmlinux tg_shares_up 22218 5.5580 vmlinux vmlinux schedule 12238 3.0614 vmlinux vmlinux mwait_idle 7395 1.8499 vmlinux vmlinux task_rq_lock 7348 1.8382 vmlinux vmlinux sock_def_readable 7202 1.8016 vmlinux vmlinux sched_clock_cpu 6981 1.7464 vmlinux vmlinux __skb_recv_datagram 6566 1.6425 vmlinux vmlinux udp_queue_rcv_skb -- 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
