Re: [Qemu-devel] [PATCH v7 6/9] qcow2: Increase the default upper limit on the L2 cache size

[Kevin Wolf]

Am 13.08.2018 um 17:16 hat Max Reitz geschrieben:
> On 2018-08-13 08:09, Leonid Bloch wrote:
> > On August 13, 2018 4:39:35 AM EEST, Max Reitz <address@hidden> wrote:
> 
> [...]
> 
> >> Ideally we'd probably want a soft and a hard cache limit, but I don't
> >> know...
> >>
> >> (Like, a soft cache limit of 1 MB with a CCI of 10 min, and a hard
> >> cache
> >> limit of 32 MB with a CCI of 1 min by default.  So whenever your cache
> >> uses more than 1 MB of RAM, your CCI is 1 min, and whenever it's below,
> >> your CCI is 10 min.)
> > 
> > Max, thanks for your insight. Indeed some good points.
> > Considering this, I'm thinking to set the limit to 16 MB, and the CCI to 5 
> > min. What do you think?
> 
> I think it's good for a preliminary solution, and then later increase
> the limit with the soft and hard limits.
> 
> OTOH, if we implement the soft/hard limits, it doesn't really matter
> what default you choose now...
> 
> > Modern Windows installations should gain performance from being able to 
> > random I/O to >8 GB chunks, and data processing tasks where each data set 
> > is 8+ GB for sure do (did benchmarks). And the maximum is only ever used if 
> > (a) the image is large enough and (b) it is indeed used.
> > While taking 256 GB images as the "limit" can be considered an overshoot, 
> > 128 GB is quite reasonable, I think.
> > 
> > Your idea with "soft" and "hard" limits is great! I'm tempted to implement 
> > this. Say 4 MB with 10 min., and 16 MB with 5 min?
> 
> 32 MB and 2 or 3 min? :-)
> 
> If you do that, I'm fine with a plain default of 32 MB for now.

I would be happy with that.

Kevin

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