Re: problems running many guests

[Karl Rister <kmr@us.ibm.com>]

On Thursday 01 May 2008 7:16:53 pm Marcelo Tosatti wrote:
> Does -no-kvm-irqchip or -no-kvm-pit makes a difference? If not, please
> grab kvm_stat --once output when that happens.

Per some suggestions I have moved up to kvm-68 which is better, but still 
having problems.  Replicating the problem with only one guest spinning has 
proven quite difficult, but attempting to boot a large smp guest can reliably 
recreate the problem.  Using -no-kvm-pit did not help the large guest 
and -no-kvm-irqchip made it seize up even earlier with only 1 cpu spinning 
instead of all of them.

>
> Also run "readprofile -r ; readprofile -m System-map-of-guest.map" with the
> host booted with "profile=kvm". Make sure all guests are running the same
> kernel image.

I got this from a spinning 16-way guest with only 8 of the host CPUs online 
and without either -no-kvm-irqchip or -no-kvm-pit:

[root@newcastle ~]# readprofile -r ; readprofile -m 
karl/System.map-2.6.25-03591-g873c05f
   101 native_read_tsc                            3.4828
     1 read_persistent_clock                      0.0192
    25 kvm_clock_read                             0.2660
    95 getnstimeofday                             0.7252
    13 update_wall_time                           0.0138
     1 second_overflow                            0.0020
readprofile: profile address out of range. Wrong map file?

The kvm_stat output during this is:

[root@newcastle ~]# kvm_stat --once
efer_reload                23354         0
exits                    3587109      2250
fpu_reload               1934298         0
halt_exits                  4583         0
halt_wakeup                   42         0
host_state_reload        2165502       167
hypercalls                  1482         0
insn_emulation            900199         0
insn_emulation_fail            0         0
invlpg                         0         0
io_exits                 1983116         0
irq_exits                 427728      2250
irq_window                     0         0
largepages                     0         0
mmio_exits                163522         0
mmu_cache_miss               176         0
mmu_flooded                   99         0
mmu_pde_zapped               191         0
mmu_pte_updated               10         0
mmu_pte_write              59030         0
mmu_recycled                   0         0
mmu_shadow_zapped             99         0
pf_fixed                   14890         0
pf_guest                       0         0
remote_tlb_flush              29         0
request_irq                    0         0
signal_exits                   1         0
tlb_flush                 481952         0

The output with -no-kvm-pit looked almost identical and with -no-kvm-pit there 
was no samples registered for either tool.

-- 
Karl Rister
IBM Linux Performance Team
kmr@us.ibm.com
(512) 838-1553 (t/l 678)

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