Messages in this thread | | | Date | Mon, 16 Aug 2010 10:27:11 -0400 | From | Andy Lutomirski <> | Subject | Re: Intel graphics CPU usage - SDVO detect bogosity? |
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[cc: intel-gfx]
Linus Torvalds wrote: > On Sun, Aug 15, 2010 at 9:06 PM, Andy Lutomirski <luto@myrealbox.com> wrote: >> You might be hitting the infamous hotplug storm [1]. The symptoms vary by >> kernel version. > > Hmm. I don't think it's a storm. The drm.debug=4 thing shows things > just every 10 seconds. That seems pretty controlled.
OK, probably not the hotplug storm. That's always been at least once per second and sometimes several for me.
> > Of course, it seems to be several milliseconds worth of work then, so > it's not _too_ controlled. I must be missing some detail. > >> If I'm right, the outputs of intel_bios_dumper and intel_bios_reader could >> be instructive (both are in intel-gpu-tools). > > My version of intel-gpu-tools must be old (fedora 12). It has > intel_gpu_dump and intel_reg_write and some other apps, but not the > bios-dumper/reader. > > Not that I could read the output of them anyway, I bet ;) > >> You could also try intel_reg_write 0x61110 0x0 and see if the problem stops >> (at least until a suspend/resume cycle). That command turns off output >> hotplug on the card, which has the side effect that the kernel will stop >> acting on bogus interrupts. > > # intel_reg_write 0x61110 0x0 > Value before: 0x4000220 > Value after: 0x0 > > but it doesn't seem to change any behavior. Still that sdvo probe > every 10 s, and still 1% of CPU for kworker in top. But that kworker > thing definitely has to be separate from the 10-second sdvo probe, > because it shows up all the time (ie top updates every second).
Almost certainly not the hotplug storm bug.
The 10 seconds is probably the timer in output_poll_execute (drm_crtc_helper.c):
#define DRM_OUTPUT_POLL_PERIOD (10*HZ)
The code in output_poll_execute (which is in your perf output) looks wrong:
list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
/* if this is HPD or polled don't check it - TV out for instance */ if (!connector->polled) continue;
else if (connector->polled & (DRM_CONNECTOR_POLL_CONNECT | DRM_CONNECTOR_POLL_DISCONNECT)) repoll = true;
[ so if we have DRM_CONNECTOR_POLL_CONNECT set we requeue the *entire* work item. or if we have DRM_CONNECTOR_POLL_DISCONNECT and it's not even connected, we still poll. ]
old_status = connector->status; /* if we are connected and don't want to poll for disconnect skip it */ if (old_status == connector_status_connected && !(connector->polled & DRM_CONNECTOR_POLL_DISCONNECT) && !(connector->polled & DRM_CONNECTOR_POLL_HPD)) continue;
[ but if the status isn't connector_status_connected, we poll it even if we're only in here due to a *different* connector ]
status = connector->funcs->detect(connector);
[ ->detect is the expensive part ]
if (old_status != status) changed = true; }
But that's really the problem, because intel_sdvo_dvi_init contains:
connector->polled = DRM_CONNECTOR_POLL_CONNECT | DRM_CONNECTOR_POLL_DISCONNECT;
I don't know if SDVO is supposed to send hotplug interrupts because that section of the docs is incomplete.
--Andy
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