Messages in this thread | | | Date | Mon, 14 Jan 2008 22:42:54 +0000 | From | "Colin Fowler" <> | 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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Hi Ingo, thanks for the reply.
Modifying /proc/sys/kernel/sched_latency_ns to be double may have in fact made things slightly worse. I used 24-rc7
Your script was only written to run for 15 seconds, so I ran it so it multiple times so it covered most of the benchmark. Other issues with these data may be that for much of the benchmark I am building data structures utilizing at most 1 to 3 cores. I'm not concerned with these timings personally as this is considered the offline part of the render. Once these data structures are built I proceed to render across 8 cores. This is the section of the benchmark I get my timings from ( I use RDTSC before and after the render segment). The majority of the overall time taken for a run is therefore data structure building. I do not time this.
Colin.
On Jan 14, 2008 6:55 PM, Ingo Molnar <mingo@elte.hu> wrote: > > * 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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