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Re: [Xen-devel] an issue with 'xm save'
On 2012-09-26 20:35, Konrad Rzeszutek Wilk wrote:
On Wed, Sep 26, 2012 at 04:48:42PM +0800, Zhenzhong Duan wrote:
Konrad Rzeszutek Wilk wrote:
On Fri, Sep 21, 2012 at 05:41:27PM +0800, Zhenzhong Duan wrote:
Hi maintainers,
I found there is an issue when 'xm save' a pvm guest. See below:
When I do save then restore once, CPU(%) in xentop showed around 99%.
When I do that second time, CPU(%) showed 199%
top in dom0 showed:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
20946 root 18 -2 10984 1284 964 S 19.8 0.3 0:48.93 block
4939 root 18 -2 10984 1288 964 S 19.5 0.3 1:34.68 block
I could kill the block process, then all look normal again.
What is the 'block' process? If you attach 'perf' to it do you get an idea
of what it is spinning at?
It's /etc/xen/scripts/block
I add 'set -x' to /etc/xen/scripts/block, found it blocked at claim_lock.
When domU was created first time, claim_lock/release_lock finished quickly,
when 'xm save' was called, claim_lock spin in its own while loop.
I can ensure no other domU create/save/etc happen when I test.
OK, so how come you have two block processes? Is it b/c you have two
disks attached to the guest? The are multiple claim_lock in the shell
script - do you know where each of two threads are spinning? Are they
spinning on the same function?
In above test, I run save/restore twice, so two block processes.
In other test, run save/restore once, there is only one block process.
After do 'xm save', I see block process spin at line 328:
321 remove)
322 case $t in
323 phy)
324 exit 0
325 ;;
326
327 file)
328 claim_lock "block"
329 node=$(xenstore_read "$XENBUS_PATH/node")
330 losetup -d "$node"
331 release_lock "block"
332 exit 0
333 ;;
thanks
zduan
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