Messages in this thread | | | Subject | Re: [PATCH v2 4/4] nmi_backtrace: generate one-line reports for idle cpus | From | Chris Metcalf <> | Date | Mon, 21 Mar 2016 13:12:39 -0400 |
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On 03/21/2016 12:32 PM, Peter Zijlstra wrote: > On Mon, Mar 21, 2016 at 12:15:12PM -0400, Chris Metcalf wrote: >> On 03/21/2016 11:42 AM, Peter Zijlstra wrote: >>> The most common idle function for x86 is: mwait_idle_with_hints(), >>> trouble is, its an inline, so I'm not sure adding __cpuidle to it does >>> anything. >> No, you're right, it wouldn't help. I didn't look at the drivers/cpuidle >> subsystem at all in my patch, since I'm not that familiar with it, >> but it seems like tagging acpi_processor_ffh_cstate_enter(), as the >> only user of mwait_idle_with_hints(), will do the job. > intel_idle() also uses it.
Ah, of course. I was only looking at the config options enabled in the kernel I was building. I've added INTEL_IDLE now and grep'ed the whole kernel tree as well, finding a couple of extra possibilities:
I do see mwait used in the ACPI 4.0 Processor Aggregator Device driver, but this seems sufficiently far removed from regular cpuidle that I don't think it's appropriate to tag the power_saving_thread() function - the initial commit talks about using the mechanism "to ride-out transient electrical and thermal emergencies."
There's also the thermal "powerclamp" driver that enforces a particular amount of idle time across the system. For this one it's less clear to me whether this is a valid "idle" state that we should ignore when doing NMI backtracing. This would be the clamp_thread() function in drivers/thermal/intel_powerclamp.c. For now I'm not including it, but what do you think?
> # nm -n ivb-ep-build/vmlinux | awk '/__cpuidle_text_start/ {p=1} {if (p) print $0} /__cpuidle_text_end/ {p=0}' > ffffffff81b16ca8 T __cpuidle_text_start > ffffffff81b16cb0 T default_idle > ffffffff81b16e50 t mwait_idle > ffffffff81b17080 t cpu_idle_poll > ffffffff81b17280 T default_idle_call > ffffffff81b172be T __cpuidle_text_end > > So no intel_idle for me..
With the changes discussed so far in this email thread, we've gotten to:
ffffffff818df178 T __cpuidle_text_start ffffffff818df180 T default_idle ffffffff818df260 t mwait_idle ffffffff818df3f0 T acpi_processor_ffh_cstate_enter ffffffff818df4a0 T default_idle_call ffffffff818df4e0 t cpu_idle_poll ffffffff818df600 t intel_idle_freeze ffffffff818df6a0 t intel_idle ffffffff818df7b5 T __cpuidle_text_end
This is about 1,600 bytes (or about 450 instructions) that will cause NMI to skip doing a backtrace if the PC is anywhere in the range.
-- Chris Metcalf, Mellanox Technologies http://www.mellanox.com
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