linux-kernel - Re: [PATCH] livepatch: Avoid CPU hogging with cond

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Date:   Mon, 10 Jan 2022 11:16:58 -0500
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Song Liu <song@...nel.org>
Cc:     David Vernet <void@...ifault.com>, live-patching@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>, jpoimboe@...hat.com,
        pmladek@...e.com, jikos@...nel.org, mbenes@...e.cz
Subject: Re: [PATCH] livepatch: Avoid CPU hogging with cond_resched

On 1/7/22 11:46 AM, Song Liu wrote:
> On Fri, Jan 7, 2022 at 6:13 AM Joe Lawrence <joe.lawrence@...hat.com> wrote:
>>
>> On 12/29/21 4:56 PM, David Vernet wrote:
>>> For example, under certain workloads, enabling a KLP patch with
>>> many objects or functions may cause ksoftirqd to be starved, and thus for
>>> interrupts to be backlogged and delayed.
>>
>> Just curious, approximately how many objects/functions does it take to
>> hit this condition?  While the livepatching kselftests are more about
>> API and kernel correctness, this sounds like an interesting test case
>> for some of the other (out of tree) test suites.
> 
> Not many patched functions. We only do small fixes at the moment. In the recent
> example, we hit the issue with ~10 patched functions. Another version
> with 2 to 3
> patched function seems fine.
> 
> Yes, I think this is an important test case.
> 

Thanks, Song.  If you can share any test setup details, I'll pass those
along to our internal QE group.  And once merged, we'll be adding this
one to the list of backports for our distro.

-- 
Joe