Time to increase MAXPHYS?

[Nikolai Lifanov]

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@
>>> 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.

- Nikolai

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