Jan Kiszka wrote: > Avi Kivity wrote: > >> Jan Kiszka wrote: >> >>> Avi Kivity wrote: >>> >>> >>>> Jan Kiszka wrote: >>>> >>>> >>>>> I ran >>>>> >>>>> user/kvmctl user/test/bootstrap user/test/smp.flat >>>>> >>>>> with the busy loop hacked into bootstrap, but I got no latency spots >>>>> this time. And what should I look for in the output of kvm_stat? >>>>> >>>>> >>>>> >>>>> >>>> The first numeric column is the total number of exits; the second is the >>>> rate of change (per second). For a spinning workload, both irq_exits >>>> and exits rate should equal the timer frequency. >>>> >>>> >>> It matches roughly, but this isn't surprising given the lack of latency >>> peaks in this scenario. >>> >>> >>> >> Okay, that's expected. But I really can't think what causes the latency >> spike you see running the bios code. 300 microseconds is enough for 3000 >> cache misses. No instruction can cause so many except rep movs and >> friends, and these are supposed to be preemptible. >> >> You might try isolating it by adding code to output markers to some I/O >> port and scattering it throughout the bios. A binary search should find >> the problem spot quickly. >> >> > > Got it! It's wbinvd from smm_init in rombios32.c! Anyone any comments on > this? >
Ha! A real life 300usec instruction! Unfortunately, it cannot be trapped on Intel (it can be trapped on AMD). Looks like a minor hole in VT, as a guest can generate very high latencies this way. For our bios, we can remove it, but there's no way to ensure an untrusted guest doesn't use it. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
