Re: [PATCH v3] blk-throtl: Introduce sync and async queues for blk-throtl

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Thu, Jan 05, 2023 at 07:35:59AM -1000, Tejun Heo <tj@xxxxxxxxxx> wrote:
> Hard limits tend to make this sort of problems a lot more pronounced because
> the existing mechanisms tend to break down for the users which are severely
> throttled down even while the device as a whole is fairly idle. cpu.max
> often triggers severe priority inversions too, so it isn't too surprising
> that people hit severe priority inversion issues w/ io.max.

To be on the same page:
1) severe PI == priority inversion across cgroups (progated e.g. via
   global locks (as with cpu.max) or FS journal (as with io.max)),
2) ordinary PI == priority inversion contained within a single cgroup,
   i.e. no different from an under-provisioned system.

The reported issue sounds like 2) but even with the separated queues 1)
is still possible :-/

> Another problem with blk-throttle is that it doesn't prioritize shared IOs
> identified by bio_issue_as_root_blkg() like iolatency and iocost do, so
> there can be very severe priority inversions when e.g. journal commit gets
> trapped in a low priority cgroup further exacerbating issues like this.

Thanks for the broader view. So the separated queues are certainly an
improvement but ultimately a mechanism based on bio_issue_as_root_blkg()
predicate and deferred throttling would be better? Or is permanent limit
enforcement more important?

Thanks,
Michal

Attachment: signature.asc
Description: Digital signature


[Index of Archives]     [Linux RAID]     [Linux SCSI]     [Linux ATA RAID]     [IDE]     [Linux Wireless]     [Linux Kernel]     [ATH6KL]     [Linux Bluetooth]     [Linux Netdev]     [Kernel Newbies]     [Security]     [Git]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Device Mapper]

  Powered by Linux