Re: High cpu usage caused by kernel process when upgraded to linux 5.19.17 or later

[Steven Rostedt]

On Mon, 3 Jul 2023 18:23:25 +0530
Vivek Anand <vivekanand754@xxxxxxxxx> wrote:

> Hi Thomas,
> 
> Further analyzing, I found that I did set
> "CONFIG_NETFILTER_XT_MATCH_LIMIT=m" in my kernel config earlier which was
> causing high CPU consumption.
> Setting it to "CONFIG_NETFILTER_XT_MATCH_LIMIT=n" resolved the high CPU
> issue.
> 
> Is there any suggestion regarding the use of this config
> "CONFIG_NETFILTER_XT_MATCH_LIMIT" as I'm getting high CPU by setting it to
> "m" ?

That config enables the compiling of: net/netfilter/xt_limit.c

The htable_gc that you reported is defined in: net/netfilter/xt_hashlimit.c

It has:

static void htable_gc(struct work_struct *work)
{
        struct xt_hashlimit_htable *ht;

        ht = container_of(work, struct xt_hashlimit_htable, gc_work.work);

        htable_selective_cleanup(ht, false);

        queue_delayed_work(system_power_efficient_wq,
                           &ht->gc_work, msecs_to_jiffies(ht->cfg.gc_interval));
}

So it queues itself every ht->cfg.gc_interval msecs. That variable seems to
come from some configuration of netfilter, and I think you can see these in:

 find /proc/sys/net -name 'gc_interval'

Perhaps you have it set off to go too much?

-- Steve


> 
> Thanks,
> Vivek
> 
> On Thu, Jun 29, 2023 at 7:48 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> 
> > On Thu, Jun 29 2023 at 12:05, Vivek Anand wrote:
> > > I've tried booting with "spectre_v2=retpoline retbleed=off".
> > > This change didn't work. Still CPU is 100%
> >
> > This does not make sense.
> >
> > retbleed=off has the same effect as CONFIG_X86_IBRS_ENTRY=n.
> >
> > The only difference is that with CONFIG_X86_IBRS_ENTRY=y and
> > retbleed=off there is one extra jump in the low level entry code
> > (syscall, interrupts, exceptions) and one extra jump on the exit side.
> >
> > But those extra jumps are completely irrelevant for the kworker threads.
> >
> > Can you please provide dmesg and the content of the files in
> >
> >  /sys/devices/system/cpu/vulnerabilities/
> >
> > on a kernel booted with "spectre_v2=retpoline retbleed=off" ?
> >
> > Thanks,
> >
> >         tglx
> >