Re: kvm guest: hrtimer: interrupt too slow

[Michael Tokarev <mjt@tls.msk.ru>]

[skip everything]

Yesterday I was "lucky" enough to actually watch what's
going on when the delay actually happens.

I run desktop environment on a kvm virtual machine here.
The server is on diskless terminal, and the rest, incl.
the window manager etc, is started from a VM.

And yesterday, during normal system load (nothing extra,
and not idle either, and all the other guests were running
under normal load too), I had a stall of everyhing on this
X session for about 2..3, maybe 5 secounds.

It felt like completely stuck machine. Nothing were moving
on the screen, no reaction to the keyboard etc.

And after several seconds it returned to normal.  With
the familiar message in dmesg -- increasing hrtimer etc,
to the next 50%.  (Without a patch from Marcelo at this
time it shuold increase min_delta to a large number).

To summarize: there's something, well, more interesting
going on here.  In addition to the scheduling issues that
causes timers to be calculated on the "wrong" CPU etc as
mentioned before, we've some real stalls somewhere, and
that only happens on SMP guests (so far anyway).

Thanks!

/mjt