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Re: [Qemu-block] [Qemu-devel] [PATCH v2 1/2] block/accounting: introduce

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v2 1/2] block/accounting: introduce latency histogram
Date: Thu, 8 Mar 2018 13:49:51 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0

On 03/08/2018 12:58 PM, Vladimir Sementsov-Ogievskiy wrote:
Hm. these numbers are actually boundary points of histogram intervals, not intervals itself. And, wiki says "The bins are usually specified as consecutive, non-overlapping intervals of a variable.", so, intervals are bins.

So, what about:

1. interval_boundaries
2. bin_boundaries
3. boundaries

(and same names with s/_/-/ for qapi)

Any of those works for me; 1 is probably most precise, while 3 is the shortest to type.

Also, now I doubt, is it a good idea to share same bin boundaries for each io type.

so, for qmp command, what about:

boundaries - optional, default boundaries for all io operations
boundaries-read - boundaries for read
boundaries-write - boundaries for write

so, call without any boundaries: drop _all_ histograms
call with only specific boundaries-*: set or reset _only_ corresponding specific histograms
call with only boundaries parameter: set or reset _all_ histograms
call with boundaries parameter and some of (or all, but it is not useful) specific boundaries-*: set or reset _all_ histograms, some to defaultĀ  and some to specific.

Seems reasonable, and if that makes the command more useful for your timing, I'm fine with it (your argument that different timing bins for read and write also makes sense, as there are some inherent differences in the amount of work done in the two directions).

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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