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Re: [Qemu-devel] [PATCH] Output dirty-bytes-rate instead of dirty-pages-

From: Daniel P. Berrange
Subject: Re: [Qemu-devel] [PATCH] Output dirty-bytes-rate instead of dirty-pages-rate
Date: Tue, 14 Mar 2017 12:37:30 +0000
User-agent: Mutt/1.7.1 (2016-10-04)

On Tue, Mar 14, 2017 at 01:29:43PM +0100, Juan Quintela wrote:
> Chao Fan <address@hidden> wrote:
> > In hmp, dirty-bytes-rate is more friendly than dirty-pages-rate.
> > It's also better for other tools to determine the cpu throttle
> > value in different architecture.
> >
> > Signed-off-by: Chao Fan <address@hidden>
> > Signed-off-by: Li Zhijian <address@hidden>
> I agree with Daniel here, you can't change the meaning of a field.  Look
> at skipped pages.  It is zero know because it is not used anymore, but
> we can't drop it.
> I think it is better to expose page_size.  We have now
> trasferred: bytes
> total: bytes
> duplicate: number of zero pages
> skipped: always zero.
> normal: number of normal pages
> normal_bytes: the same  in bytes
> mbps: megabytes per second?  I can't even remember this one
> dirty_sync_count: number of times we have go through the whole memory
> postcopy_requests = number of pages asked by postcopy faults?
> dirty_pages_rate = pages by some kind of unit
> And we haven't yet started with compression or xbzrle.  I think that the
> best approach at this point is putting everything in pages except the
> things that don't make sense.
> We can put everything on bytes, but then everything is HUGE.
> Anyways, what do libvirt/management apps preffer?

Since we have many fields already which are reported as page counts, I
think just adding page size would be preferrable to having twice as many
fields reported duplicating bytes + pages.

The only reason to favour duplicating all fields to report bytes, is if
we needed to vary page size to deal with huge pages (eg if some reported
pages were 4kb and other reported pages with 2MB). You can easily just
scale huge pages counts to be "normal"  pages for purpose of reporting
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