Messages in this thread | | | Date | Thu, 2 Sep 2021 09:16:50 +0200 | From | Sebastian Andrzej Siewior <> | Subject | Re: [PATCH v2] trace: Add migrate-disabled counter to tracing output. |
| |
On 2021-08-10 15:26:26 [+0200], To Steven Rostedt wrote: > From: Thomas Gleixner <tglx@linutronix.de> > > migrate_disable() forbids task migration to another CPU. It is available > since v5.11 and has already users such as highmem or BPF. It is useful > to observe this task state in tracing which already has other states > like the preemption counter. > > Instead of adding the migrate disable counter as a new entry to struct > trace_entry, which would extend the whole struct by four bytes, it is > squashed into the preempt-disable counter. The lower four bits represent > the preemption counter, the upper four bits represent the migrate > disable counter. Both counter shouldn't exceed 15 but if they do, there > is a safety net which caps the value at 15. > > Add the migrate-disable counter to the trace entry so it shows up in the > trace. Due to the users mentioned above, it is already possible to > observe it: > > | bash-1108 [000] ...21 73.950578: rss_stat: mm_id=2213312838 curr=0 type=MM_ANONPAGES size=8192B > | bash-1108 [000] d..31 73.951222: irq_disable: caller=flush_tlb_mm_range+0x115/0x130 parent=ptep_clear_flush+0x42/0x50 > | bash-1108 [000] d..31 73.951222: tlb_flush: pages:1 reason:local mm shootdown (3) > > The last value is the migrate-disable counter. > > Things that popped up: > - trace_print_lat_context() does not print the migrate counter. Not sure > if it should. It is used in "verbose" mode and uses 8 digits and I'm > not sure ther is something processing the value. > > - trace_define_common_fields() now defines a different variable. This > probably breaks things. No ide what to do in order to preserve the old > behaviour. Since this is used as a filter it should be split somehow > to be able to match both nibbles here. > > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > [bigeasy: patch description.] > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > --- > v1…v2: > - use the upper nibble of the preemption counter for the migrate > disable counter and the lower for the preemption counter. This > avoids extending the struct by four bytes due to alignment / > padding.
Ping.
Sebastian
| |