On 25.07.2025 20:55, Steven Rostedt wrote: > From: Josh Poimboeuf <[email protected]> > > Cache the results of the unwind to ensure the unwind is only performed > once, even when called by multiple tracers. > > The cache nr_entries gets cleared every time the task exits the kernel. > When a stacktrace is requested, nr_entries gets set to the number of > entries in the stacktrace. If another stacktrace is requested, if > nr_entries is not zero, then it contains the same stacktrace that would be > retrieved so it is not processed again and the entries is given to the > caller. > > Co-developed-by: Steven Rostedt (Google) <[email protected]> > Signed-off-by: Josh Poimboeuf <[email protected]> > Signed-off-by: Steven Rostedt (Google) <[email protected]>
Reviewed-by: Jens Remus <[email protected]> > diff --git a/kernel/unwind/deferred.c b/kernel/unwind/deferred.c > + cache = info->cache; > + trace->entries = cache->entries; > + > + if (cache->nr_entries) { > + /* > + * The user stack has already been previously unwound in this > + * entry context. Skip the unwind and use the cache. > + */ > + trace->nr = cache->nr_entries; > + return 0; > + } > + > trace->nr = 0; > - trace->entries = info->entries; > unwind_user(trace, UNWIND_MAX_ENTRIES); > > + cache->nr_entries = trace->nr; > + Would the following alternative to above excerpt be easier to read? /* Use the cache, if the user stack has already been previously * unwound in this entry context. If not this will initialize * trace->nr to zero to trigger the unwind now. */ cache = info->cache; trace->nr = cache->nr_entries; trace->entries = cache->entries; if (!trace->nr) { unwind_user(trace, UNWIND_MAX_ENTRIES); cache->nr_entries = trace->nr; } > return 0; > } Regards, Jens -- Jens Remus Linux on Z Development (D3303) +49-7031-16-1128 Office [email protected] IBM IBM Deutschland Research & Development GmbH; Vorsitzender des Aufsichtsrats: Wolfgang Wendt; Geschäftsführung: David Faller; Sitz der Gesellschaft: Böblingen; Registergericht: Amtsgericht Stuttgart, HRB 243294 IBM Data Privacy Statement: https://www.ibm.com/privacy/
