On 10/10/2011 09:01 PM, Alexander Graf wrote:
For example, one execution of QEMU produced the following log:
$ stap qemu-timing.stp 0.000 Start 0.036 Run 0.038 BIOS post 0.180 BIOS int 19 0.181 BIOS boot OS 0.181 LinuxBoot copy kernel 1.371 LinuxBoot copy initrd
Yeah, there was a thread a bit ago about the performance of the interface to read the kernel/initrd. I think at it was using single byte access instructions and there were patches to use string accessors instead? I can't remember where that threaded ended up.
IIRC we're already using string accessors, but are still slow. Richard had a nice patch cooked up to basically have the fw_cfg interface be able to DMA its data to the guest. I like the idea. Avi did not.
And yes, bad -kernel performance does hurt in some workloads. A lot.
The rep/ins implementation is still slow, optimizing it can help.
What does 'perf top' say when running this workload?