Re: Time to increase MAXPHYS?

On Fri, Sep 15, 2017 at 9:18 AM, Nikolai Lifanov <lifanov_at_freebsd.org>
wrote:

> On 6/3/17 11:55 PM, Allan Jude wrote:
> > On 2017-06-03 22:35, Julian Elischer wrote:
> >> On 4/6/17 4:59 am, Colin Percival wrote:
> >>> On January 24, 1998, in what was later renumbered to SVN r32724, dyson_at_
> >>> wrote:
> >>>> Add better support for larger I/O clusters, including larger physical
> >>>> I/O.  The support is not mature yet, and some of the underlying
> >>>> implementation
> >>>> needs help.  However, support does exist for IDE devices now.
> >>> and increased MAXPHYS from 64 kB to 128 kB.  Is it time to increase it
> >>> again,
> >>> or do we need to wait at least two decades between changes?
> >>>
> >>> This is hurting performance on some systems; in particular, EC2 "io1"
> >>> disks
> >>> are optimized for 256 kB I/Os, EC2 "st1" (throughput optimized
> >>> spinning rust)
> >>> disks are optimized for 1 MB I/Os, and Amazon's NFS service (EFS)
> >>> recommends
> >>> using a maximum I/O size of 1 MB (and despite NFS not being *physical*
> >>> I/O it
> >>> seems to still be limited by MAXPHYS).
> >>>
> >> We increase it in freebsd 8 and 10.3 on our systems,  Only good results.
> >>
> >> sys/sys/param.h:#define MAXPHYS         (1024 * 1024)   /* max raw I/O
> >> transfer size */
> >>
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> >
> > At some point Warner and I discussed how hard it might be to make this a
> > boot time tunable, so that big amd64 machines can have a larger value
> > without causing problems for smaller machines.
> >
> > ZFS supports a block size of 1mb, and doing I/Os in 128kb negates some
> > of the benefit.
> >
> > I am preparing some benchmarks and other data along with a patch to
> > increase the maximum size of pipe I/O's as well, because using 1MB
> > offers a relatively large performance gain there as well.
> >
>
> Hi!
>
> I also migrated to 1mb recordsize. What's the status of your patches
> and/or making MAXPHYS a boot-time tunable? I can help test these.
>

Still in my queue to do.

Warner