git: 812c9f48a2b7 - main - Save context switch per I/O for iSCSI and IOCTL frontends.

[Alan Somers]

On Thu, Feb 18, 2021 at 8:29 PM Alexander Motin <mav at freebsd.org> wrote:

> The branch main has been updated by mav:
>
> URL:
> https://cgit.FreeBSD.org/src/commit/?id=812c9f48a2b7bccc31b2a6077b299822357832e4
>
> commit 812c9f48a2b7bccc31b2a6077b299822357832e4
> Author:     Alexander Motin <mav at FreeBSD.org>
> AuthorDate: 2021-02-19 03:07:32 +0000
> Commit:     Alexander Motin <mav at FreeBSD.org>
> CommitDate: 2021-02-19 03:29:38 +0000
>
>     Save context switch per I/O for iSCSI and IOCTL frontends.
>
>     Introduce new CTL core KPI ctl_run(), preprocessing I/Os in the caller
>     context instead of scheduling another thread just for that.  This call
>     may sleep, that is not acceptable for some frontends like the original
>     CAM/FC one, but iSCSI already has separate sleepable per-connection RX
>     threads, and another thread scheduling is mostly just a waste of time.
>     IOCTL frontend actually waits for the I/O completion in the caller
>     thread, so the use of another thread for this has even less sense.
>
>     With this change I can measure ~5% IOPS improvement on 4KB iSCSI I/Os
>     to ZFS.
>

Cool!  That sounds very useful.