Re: [PATCH v3 3/4] xen/console: add build-time rate-limiting controls

[dmukhin@xxxxxxxx]

On Fri, Jul 17, 2026 at 07:34:39PM -0700, dmukhin@xxxxxxxx wrote:
> On Thu, Jul 16, 2026 at 11:59:34AM +0200, Teddy Astie wrote:
> > Le 15/07/2026 à 22:24, dmukhin@xxxxxxxx a écrit :
> > > From: Denis Mukhin <dmukhin@xxxxxxxx>
> > > 
> > > Introduce CONFIG_PRINTK_RATELIMIT_MS and CONFIG_PRINTK_RATELIMIT_BURST
> > > for configuring rate-limiting policy at the compile time.
> > > 
> > > Use symbols for global rate-limiting initialization in the console driver.
> > > 
> > > Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
> > > ---
> > > Changes since v2:
> > > - moved rate-limiting controls to common/Kconfig
> > > ---
> > >   xen/common/Kconfig         | 29 +++++++++++++++++++++++++++++
> > >   xen/drivers/char/console.c |  6 ++++--
> > >   2 files changed, 33 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/xen/common/Kconfig b/xen/common/Kconfig
> > > index da80fdba8469..fd22806884e0 100644
> > > --- a/xen/common/Kconfig
> > > +++ b/xen/common/Kconfig
> > > @@ -672,4 +672,33 @@ config PM_STATS
> > >             Enable collection of performance management statistics to aid 
> > > in
> > >             analyzing and tuning power/performance characteristics of the 
> > > system
> > > +menu "Console rate-limiting"
> > > +
> > > +config PRINTK_RATELIMIT_MS
> > > + int "printk rate-limiting time window (milliseconds)"
> > > + default 5000
> > > + help
> > > +   Specifies the time window, in milliseconds, for rate-limited printk
> > > +   messages. No more than `CONFIG_PRINTK_RATELIMIT_BURST` messages will 
> > > be
> > > +   printed within this window.
> > > +
> > > +   Setting this value to 0 disables rate-limiting entirely.
> > > +
> > > +   Rate-limited messages are those controlled by the `loglvl` and
> > > +   `guest_loglvl` command-line parameters.
> > > +
> > > +config PRINTK_RATELIMIT_BURST
> > > + int "printk rate-limited message burst size"
> > > + default 10
> > > + help
> > > +   Defines the maximum number of rate-limited printk messages that may be
> > > +   printed within each `CONFIG_PRINTK_RATELIMIT_MS` time window.
> > > +
> > > +   Setting this value to 0 disables rate-limiting entirely.
> > > +
> > > +   Rate-limited messages are those controlled by the `loglvl` and
> > > +   `guest_loglvl` command-line parameters.
> > > +
> > > +endmenu
> > > +
> > >   endmenu
> > 
> > Given that setting 0 to either will disable rate limiting, would it be
> > preferable instead to have a more general PRINTK_RATELIMIT toggle, where :
> > 
> > Setting it to true would enable configuration of ms and burst (rejecting 0
> > if possible).
> > Setting it to false would set both to 0 hence disabling rate limiting by
> > default.
> > 
> > And we do something like
> > 
> > static const unsigned int printk_ratelimit_ms =
> >   IS_ENABLED(CONFIG_PRINTK_RATELIMIT) ? CONFIG_PRINTK_RATELIMIT_MS : 0;
> > 
> > (similarly for burst)
> > 
> > ?
> 
> I can hide both selectors behind CONFIG_PRINTK_RATELIMIT.

Oh, I haven't seen Jan's feedback on that suggestion before answering.

TBH, I am fine either way, but I think just having _some_ controls is more
than enough for now given that there's no certainty on how ratelimiting will
evolve...