[pve-devel] diskstats : wchar vs write_bytes

[Alexandre DERUMIER]

Ok, I done more test with disk writethrough=on, and rchar/wchar is ok.
So it must be related to write flushed.

I thinked to implement disk stats from "info blockstats" with qmp ,it should be fast (parallel http request).
What do you think about it ?




rchar: 757183294269
wchar: 347303242382
syscr: 129630950
syscw: 56943947
read_bytes: 144189434880
write_bytes: 351250344960
cancelled_write_bytes: 0

*

# info blockstats
drive-virtio0: rd_bytes=1318046208 wr_bytes=244297728 rd_operations=49168 wr_operations=42677 flush_operations=6138 
drive-virtio1: rd_bytes=757655435776 wr_bytes=348037467136 rd_operations=4802336 wr_operations=4793844 flush_operations=0 


----- Mail original ----- 

De: "Alexandre DERUMIER" <aderumier at odiso.com> 
À: "Dietmar Maurer" <dietmar at proxmox.com> 
Cc: pve-devel at pve.proxmox.com 
Envoyé: Samedi 28 Avril 2012 09:11:04 
Objet: Re: [pve-devel] diskstats : wchar vs write_bytes 

I read the doc, for reads I understand 

rchar : read from the real underlying storage 
read_bytes : read from kvm host buffer cache 

but for writes I don't understand... 
I don't use writeback, so data should be write directly to storage. 

vm use cache=none. 

So data must be write to the cache of the storage, then flushed each time the vm do a fsync, or barrier occur. 
I'll try to do some tests with writethrough to see how are stats. 

Thanks 

Alexandre 


----- Mail original ----- 

De: "Dietmar Maurer" <dietmar at proxmox.com> 
À: "Alexandre DERUMIER" <aderumier at odiso.com>, pve-devel at pve.proxmox.com 
Envoyé: Samedi 28 Avril 2012 09:05:11 
Objet: RE: [pve-devel] diskstats : wchar vs write_bytes 

> I was checking rrd io stats for a vm I was installing, and something strange. 
> 
> I have a lot of writes, but 
> wchar < rchar 
> but 
> write_bytes > read_bytes 
> 
> 
> write_bytes,read_bytes seem to be the correct values, reported in qemu 
> monitor also 
> I also check on my storage,write_bytes is the correct value. 
> 
> what's the difference between wchar and write_bytes ? 

Cache? Details are available here: 

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blob;f=Documentation/filesystems/proc.txt;h=b7413cb46dcb1f1a331068861e766a6c03a5da40;hb=HEAD#l1387 

- Dietmar 




-- 

-- 




Alexandre D erumier 
Ingénieur Système 
Fixe : 03 20 68 88 90 
Fax : 03 20 68 90 81 
45 Bvd du Général Leclerc 59100 Roubaix - France 
12 rue Marivaux 75002 Paris - France 

_______________________________________________ 
pve-devel mailing list 
pve-devel at pve.proxmox.com 
http://pve.proxmox.com/cgi-bin/mailman/listinfo/pve-devel 



-- 

-- 




	Alexandre D erumier 
Ingénieur Système 
Fixe : 03 20 68 88 90 
Fax : 03 20 68 90 81 
45 Bvd du Général Leclerc 59100 Roubaix - France 
12 rue Marivaux 75002 Paris - France