On Wed, 2019-07-31 at 14:24 +0800, Fuqian Huang wrote:
> In drivers/gpu/drm/amd/amdgpu/amdgpu_ih.c,
> amdgpu_ih_process calls DRM_DEBUG which calls drm_dbg and
> finally calls printk.
> As amdgpu_ih_process is called from an interrupt handler,
> and interrupt handler should be short as possible.
>
> As printk may lead to bogging down the system or can even
> create a live lock. printk should not be used in IRQ context.
> Instead, trace_printk is recommended in IRQ context.
> Link: https://lwn.net/Articles/365835
>
> Reviewed-by: Joe Perches <[email protected]>
I made a suggestion. I did not review this.
Please do not add signatures like this if
not specifically given by someone.
> Signed-off-by: Fuqian Huang <[email protected]>
> ---
> Changes in v2:
> - Only make the interrupt uses the trace_printk to avoid
> all 4000+ drm_dbg/DRM_DEBUG uses emitting a trace_printk.
>
> drivers/gpu/drm/drm_print.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
> index a17c8a14dba4..747835d16fa6 100644
> --- a/drivers/gpu/drm/drm_print.c
> +++ b/drivers/gpu/drm/drm_print.c
> @@ -236,9 +236,13 @@ void drm_dbg(unsigned int category, const char *format, ...)
> vaf.fmt = format;
> vaf.va = &args;
>
> - printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
> - __builtin_return_address(0), &vaf);
> -
> + if (in_interrupt()) {
> + trace_printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
> + __builtin_return_address(0), &vaf);
> + } else {
> + printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
> + __builtin_return_address(0), &vaf);
> + }
> va_end(args);
> }
> EXPORT_SYMBOL(drm_dbg);
On Tue, Jul 30, 2019 at 11:26:32PM -0700, Joe Perches wrote:
> On Wed, 2019-07-31 at 14:24 +0800, Fuqian Huang wrote:
> > In drivers/gpu/drm/amd/amdgpu/amdgpu_ih.c,
> > amdgpu_ih_process calls DRM_DEBUG which calls drm_dbg and
> > finally calls printk.
> > As amdgpu_ih_process is called from an interrupt handler,
> > and interrupt handler should be short as possible.
> >
> > As printk may lead to bogging down the system or can even
> > create a live lock. printk should not be used in IRQ context.
> > Instead, trace_printk is recommended in IRQ context.
> > Link: https://lwn.net/Articles/365835
> >
> > Reviewed-by: Joe Perches <[email protected]>
>
> I made a suggestion. I did not review this.
>
> Please do not add signatures like this if
> not specifically given by someone.
+1
> > Signed-off-by: Fuqian Huang <[email protected]>
> > ---
> > Changes in v2:
> > - Only make the interrupt uses the trace_printk to avoid
> > all 4000+ drm_dbg/DRM_DEBUG uses emitting a trace_printk.
> >
> > drivers/gpu/drm/drm_print.c | 10 +++++++---
> > 1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
> > index a17c8a14dba4..747835d16fa6 100644
> > --- a/drivers/gpu/drm/drm_print.c
> > +++ b/drivers/gpu/drm/drm_print.c
> > @@ -236,9 +236,13 @@ void drm_dbg(unsigned int category, const char *format, ...)
Right above here is a check for drm_debug, which defaults to off, so in
production this all has 0 impact. But changing all the debug output from
dmesg to tracing is sure to break everyone's CI and test setups.
I'm all for cleaning up the drm logging stuff (it's a real mess), but it's
a very delicate house of cards and with thousands of users, not easy to
change. Unfortunately I don't really have a solid recommendation for what
the ideal drm logging should look like. Plus we already have a pile of
competing approaches ...
-Daniel
> > vaf.fmt = format;
> > vaf.va = &args;
> >
> > - printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
> > - __builtin_return_address(0), &vaf);
> > -
> > + if (in_interrupt()) {
> > + trace_printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
> > + __builtin_return_address(0), &vaf);
> > + } else {
> > + printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
> > + __builtin_return_address(0), &vaf);
> > + }
> > va_end(args);
> > }
> > EXPORT_SYMBOL(drm_dbg);
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch