Re: [PATCH v2 0/3] optimize waiting for free thread to do compression

[Markus Armbruster <armbru@redhat.com>]

guangrong.xiao@gmail.com writes:

> From: Xiao Guangrong <xiaoguangrong@tencent.com>
>
> Changelog in v2:
> squash 'compress-wait-thread-adaptive' into 'compress-wait-thread' based
> on peter's suggestion
>
>
> Currently we have two behaviors if all threads are busy to do compression,
> the main thread mush wait one of them becoming free if @compress-wait-thread
> set to on or the main thread can directly return without wait and post
> the page out as normal one
>
> Both of them have its profits and short-comes, however, if the bandwidth is
> not limited extremely so that compression can not use out all of it bandwidth,
> at the same time, the migration process is easily throttled if we posted too
> may pages as normal pages. None of them can work properly under this case
>
> In order to use the bandwidth more effectively, we introduce the third
> behavior, adaptive, which make the main thread wait
> if there is no bandwidth left or let the page go out as normal page if there
> has enough bandwidth to make sure the migration process will not be
> throttled
>
> Another patch introduces a new statistic, pages-per-second, as bandwidth
> or mbps is not enough to measure the performance of posting pages out as
> we have compression, xbzrle, which can significantly reduce the amount of
> the data size, instead, pages-per-second is the one we want
>
> Performance data
> ================
> We have limited the bandwidth to 300
>
>                                 Used Bandwidth     Pages-per-Second
> compress-wait-thread = on         951.66 mbps         131784
>
> compress-wait-thread = off        2491.74 mbps        93495
> compress-wait-thread-adaptive     1982.94 mbps        162529
>    = on

I think you mean compress-wait-thread = adaptive here.

Can you sketch use cases for all three settings?  The resulting guidance
should then be worked into documentation.