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Re: Some performance numbers for virtiofs, DAX and virtio-9p

From: Miklos Szeredi
Subject: Re: Some performance numbers for virtiofs, DAX and virtio-9p
Date: Thu, 10 Dec 2020 20:29:21 +0100

On Thu, Dec 10, 2020 at 5:11 PM Vivek Goyal <vgoyal@redhat.com> wrote:

> Conclusion
> -----------
> - virtiofs DAX seems to help a lot in many workloads.
>   Note, DAX performance well only if data fits in cache window. My total
>   data is 16G and cache window size is 16G as well. If data is larger
>   than DAX cache window, then performance of dax suffers a lot. Overhead
>   of reclaiming old mapping and setting up a new one is very high.

Which begs the question: what is the optimal window size?

What is the cost per GB of window to the host and guest?

Could we measure at what point does a large window size actually make
performance worse?

> NAME                    WORKLOAD                Bandwidth       IOPS
> 9p-none                 seqread-psync           98.6mb          24.6k
> 9p-mmap                 seqread-psync           97.5mb          24.3k
> 9p-loose                seqread-psync           91.6mb          22.9k
> vtfs-none               seqread-psync           98.4mb          24.6k
> vtfs-none-dax           seqread-psync           660.3mb         165.0k
> vtfs-auto               seqread-psync           650.0mb         162.5k
> vtfs-auto-dax           seqread-psync           703.1mb         175.7k
> vtfs-always             seqread-psync           671.3mb         167.8k
> vtfs-always-dax         seqread-psync           687.2mb         171.8k
> 9p-none                 seqread-psync-multi     397.6mb         99.4k
> 9p-mmap                 seqread-psync-multi     382.7mb         95.6k
> 9p-loose                seqread-psync-multi     350.5mb         87.6k
> vtfs-none               seqread-psync-multi     360.0mb         90.0k
> vtfs-none-dax           seqread-psync-multi     2281.1mb        570.2k
> vtfs-auto               seqread-psync-multi     2530.7mb        632.6k
> vtfs-auto-dax           seqread-psync-multi     2423.9mb        605.9k
> vtfs-always             seqread-psync-multi     2535.7mb        633.9k
> vtfs-always-dax         seqread-psync-multi     2406.1mb        601.5k

Seems like in all the -multi tests 9p-none performs consistently
better than vtfs-none.   Could that be due to the single queue?


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