svn commit: r309714 - head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs

[Andriy Gapon]

On 14/12/2016 21:49, Alexander Motin wrote:
> On 14.12.2016 14:03, Andriy Gapon wrote:
>> On 08/12/2016 17:58, Alexander Motin wrote:
>>>   This change switches zio_timestamp_compare() from comparing uninitialized
>>>   io_offset to really populated io_bookmark values.  I haven't decided yet
>>>   what to do with timestampts, but on simple tests this change gives the
>>>   same peformance results by just making code to work as declared.
>>
>> I think that we should just enable precise timestamps.
>> I just can't see them noticeably hurting performance given the amount of
>> calculations, memory allocations, locking, etc, that ZFS already has.
>> And there are layers above and below ZFS too.
> 
> It is orthogonal to this change and can be done any time, if decided.

Yes, indeed.

> I worried mostly about some older systems still using HPET or ACPI
> timecounters, where half dozen extra timer calls per single I/O may be
> quite expensive.
> 
> I've recently reviewed all places where ZFS calls gethrtime(), and found
> that in most of them precision is not needed, even 1 second would be
> enough, not even 1/hz.  I've found only two cases where precision is
> important, both about ZIO sorting in different places (this is one of
> the two), and both of them are now workarounded now by using offset as
> secondary key.

Thank you for looking into this and fixing the bug!

-- 
Andriy Gapon