[Ksummit-discuss] [TECH TOPIC] Addressing long-standing high-latency problems related to I/O

[Jan Kara]

On Fri 16-09-16 22:13:44, Paolo Valente wrote:
> > Il giorno 16 set 2016, alle ore 21:36, James Bottomley <James.Bottomley at HansenPartnership.com> ha scritto:
> > 
> > On Fri, 2016-09-16 at 20:48 +0200, Paolo Valente wrote:
> >>> Il giorno 16 set 2016, alle ore 17:15, James Bottomley <
> >>> James.Bottomley at HansenPartnership.com> ha scritto:
> >>> 
> >>> On Fri, 2016-09-16 at 10:24 +0200, Greg KH wrote:
> >>>> On Fri, Sep 16, 2016 at 09:55:45AM +0200, Paolo Valente wrote:
> >>>>> Linux systems suffers from long-standing high-latency problems, 
> >>>>> at system and application level, related to I/O.  For example,
> >>>>> they usually suffer from poor responsiveness--or even 
> >>>>> starvation, depending on the workload--while, e.g., one or more 
> >>>>> files are being read/written/copied.  On a similar note, 
> >>>>> background workloads may cause audio/video playback/streaming 
> >>>>> to stutter, even with long gaps. A lot of test results on this 
> >>>>> problem can be found here [1] (I'm citing only this resource 
> >>>>> just because I'm familiar with it, but evidence can be found in 
> >>>>> countless technical reports, scientific papers, forum
> >>>>> discussions, and so on).
> >>>> 
> >>>> <snip>
> >>>> 
> >>>> Isn't this a better topic for the Vault conference, or the 
> >>>> storage mini conference?
> >>> 
> >>> LSF/MM would be the place to have the technical discussion, yes. 
> >>> It will be in Cambridge (MA,USA not the real one) in the Feb/March
> >>> time frame in 2017.  Far more of the storage experts (who likely 
> >>> want to weigh in) will be present.
> >>> 
> >> 
> >> Perfect venue.  Just it would be a pity IMO to waste the opportunity
> >> of my being at KS with other people working on the components 
> >> involved in high-latency issues, and to delay by more months a 
> >> discussion on possible solutions.
> > 
> > OK, so the problem with a formal discussion of something like this at
> > KS is that of the 80 or so people in the room, likely only 10 have any
> > interest whatsoever, leading to intense boredom for the remaining 70.
> 
> No no, that would be scary to me, given the level of the audience!  I
> thought it would have been possible to arrange some sort of
> sub-discussions with limited groups (although maybe the fact the Linux
> still suffers from high latencies might somehow worry all people that
> care about the kernel).  I'm sorry, but this will be my first time at KS.

Yeah, so I'll be at KS and I'd be interested in this discussion. Actually
I expect to have Jens Axboe and Christoph Hellwig around as well which are
biggest blk-mq proponents so I think the most important people for the
discussion about what are the blockers for merging are there.

I agree that for a discussion about details of the scheduling algorithm
LSF/MM is a better venue but at least for a process discussion under which
conditions BFQ is mergeable KS is OK.

								Honza
-- 
Jan Kara <jack at suse.com>
SUSE Labs, CR