linux-kernel - Re: [RFC PATCH] blk-throttle: add burst allowance.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20171117192614.4knf72v26iir6tpi@kernel.org>
Date:   Fri, 17 Nov 2017 11:26:14 -0800
From:   Shaohua Li <shli@...nel.org>
To:     Khazhismel Kumykov <khazhy@...gle.com>
Cc:     axobe@...nel.dk, shli@...com, vgoyal@...hat.com, tj@...nel.org,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org
Subject: Re: [RFC PATCH] blk-throttle: add burst allowance.

On Thu, Nov 16, 2017 at 08:25:58PM -0800, Khazhismel Kumykov wrote:
> On Thu, Nov 16, 2017 at 8:50 AM, Shaohua Li <shli@...nel.org> wrote:
> > On Tue, Nov 14, 2017 at 03:10:22PM -0800, Khazhismel Kumykov wrote:
> >> Allows configuration additional bytes or ios before a throttle is
> >> triggered.
> >>
> >> This allows implementation of a bucket style rate-limit/throttle on a
> >> block device. Previously, bursting to a device was limited to allowance
> >> granted in a single throtl_slice (similar to a bucket with limit N and
> >> refill rate N/slice).
> >>
> >> Additional parameters bytes/io_burst_conf defined for tg, which define a
> >> number of bytes/ios that must be depleted before throttling happens. A
> >> tg that does not deplete this allowance functions as though it has no
> >> configured limits. tgs earn additional allowance at rate defined by
> >> bps/iops for the tg. Once a tg has *_disp > *_burst_conf, throttling
> >> kicks in. If a tg is idle for a while, it will again have some burst
> >> allowance before it gets throttled again.
> >>
> >> slice_end for a tg is extended until io_disp/byte_disp would fall to 0,
> >> when all "used" burst allowance would be earned back. trim_slice still
> >> does progress slice_start as before and decrements *_disp as before, and
> >> tgs continue to get bytes/ios in throtl_slice intervals.
> >
> > Can you describe why we need this? It would be great if you can describe the
> > usage model and an example. Does this work for io.low/io.max or both?
> >
> > Thanks,
> > Shaohua
> >
> 
> Use case that brought this up was configuring limits for a remote
> shared device. Bursting beyond io.max is desired but only for so much
> before the limit kicks in, afterwards with sustained usage throughput
> is capped. (This proactively avoids remote-side limits). In that case
> one would configure in a root container io.max + io.burst, and
> configure low/other limits on descendants sharing the resource on the
> same node.
> 
> With this patch, so long as tg has not dispatched more than the burst,
> no limit is applied at all by that tg, including limit imposed by
> io.low in tg_iops_limit, etc.

I'd appreciate if you can give more details about the 'why'. 'configuring
limits for a remote shared device' doesn't justify the change.