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Re: [Qemu-devel] Question about vNVDIMM file format
From: |
Richard W.M. Jones |
Subject: |
Re: [Qemu-devel] Question about vNVDIMM file format |
Date: |
Wed, 18 May 2016 18:36:33 +0100 |
User-agent: |
Mutt/1.5.20 (2009-12-10) |
I thought you might be interested in some performance results, "hot
off the presses".
With DAX enabled, I see the following messages in the guest kernel
logs, which I assume means it is working:
[ 0.469364] EXT4-fs (pmem0): DAX enabled. Warning: EXPERIMENTAL, use at your
own risk
[ 0.469932] EXT4-fs (pmem0): mounting ext2 file system using the ext4
subsystem
[ 0.470682] EXT4-fs (pmem0): mounted filesystem without journal. Opts: dax
Enabling vNVDIMM + ext4.ko + DAX for the libguestfs appliance[1] root
disk improves our boot+shutdown performance measure[2] by between 20
and 30 milliseconds, which is about 5% faster at the moment.
I also wanted to know if memory usage is reduced. I ran `free -m'
inside a freshly booted appliance.
Without DAX:
$ free -m
total used free shared buff/cache available
Mem: 485 3 451 1 30 465
Swap: 0 0 0
With DAX:
$ free -m
total used free shared buff/cache available
Mem: 485 3 469 1 12 467
Swap: 0 0 0
I also wanted to know if qemu's memory usage is reduced. I captured
the rusage.ru_maxrss of the qemu subprocess with and without DAX. The
difference is only about 5 MB, which doesn't seem like very much to
me. Perhaps I'm measuring this wrong.
If you have better suggestions for measuring memory usage, please let
me know.
Rich.
[1] http://libguestfs.org/guestfs-internals.1.html#architecture
[2]
http://libguestfs.org/guestfs-performance.1.html#baseline:-starting-the-appliance
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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