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From: | Paolo Bonzini |
Subject: | Re: [Qemu-devel] Fedora FC21 - Bug: 100% CPU and hangs in gettimeofday(&tp, NULL); forever |
Date: | Tue, 13 Jan 2015 22:16:08 +0100 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 |
On 13/01/2015 22:14, Gerhard Wiesinger wrote: > > I also had a look at the kernel code again: > http://lxr.free-electrons.com/source/kernel/time/timekeeping.c?v=3.17#L493 > 499 do { > 500 seq = read_seqcount_begin(&tk_core.seq); > 501 > 502 ts->tv_sec = tk->xtime_sec; > 503 nsecs = timekeeping_get_ns(&tk->tkr); > 504 > 505 } while (read_seqcount_retry(&tk_core.seq, seq)); > > So it looks like that the seqcount always changes and therefore loops > forever here (as far as I digged it down this is the only loop here). > > Might be something wrong with the memory barriers in recent qemu-kvm > releases? No, that's not possible. Unless you pause/resume or migrate the VM, all of the handling of kvmclock is entirely in the kernel. Paolo
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