Messages in this thread | | | Date | Mon, 14 Jan 2008 19:55:20 +0100 | From | Ingo Molnar <> | Subject | Re: Performance loss 2.6.22->22.6.23->2.6.24-rc7 on CPU intensive benchmark on 8 Core Xeon |
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* Colin Fowler <elethiomel@gmail.com> wrote:
> Benchmark : A ray-trace is performed on 500 times on 17 separate > scenes. Workload is distributed by tiling the framebuffer into N 32x32 > pixel tiles. Each CPU grabs one of N tiles out of the queue and > repeats until no jobs are left. Rendering is to a shared framebuffer > (obviously this causes problems with caching). Locking and > synchronization is done using pthreads. > > Other details: The system is cleanly booted for each run. No I/O is > performed during the timed portions of the test. The benchmark does > however read a model file from the drive and build a data structure > from it before each timed portion. > > On the 2.6.22 series of kernels results are pretty much the same. On > 2.6.23 series kernels I see a loss in speed of ~2% across the board. > On 2.6.24-rc7 that loss in speed is perhaps very slightly worse (~3%). > 2.6.22 Kernels tested: 22.9(Ubuntu Stock Kernel), 22.14, 22.15 > 2.6.23 Kernels tested: 23.1, 23.3, 23.13 > 2.6.24 Kernels tested: 24-rc7 > > I have my kernel compiled to use the SLAB allocator. All other > tweaking options are set as defaults. My config files are available at > http://vangogh.cs.tcd.ie/fowler/configs . Perhaps I'm configuring > something wrong for the type of work I do?
Could you try CONFIG_SCHED_DEBUG=y and CONFIG_SCHEDSTATS=y and double the value of /proc/sys/kernel/sched_latency_ns - does that make any difference? Please also run the following script while the ray-trace app is running:
http://people.redhat.com/mingo/cfs-scheduler/tools/cfs-debug-info.sh
and send me the output of it, so that we can have an idea about what's going on in your system during this workload.
Ingo
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