This is rather on the obvious side.
While doing strace on an executable using libunwind, I noticed a
lot of:
msync(0, 1, MS_SYNC) = -1 ENOMEM (Cannot allocate memory)
Since we know that the first page isn't mapped (or at least doesn't
contain the data we are looking for), we can eliminate all such
msync calls.
Tested on Linux/x86_64 with no regressions.
Original code was accessing rs_cache memory without holding a lock
in some cases. If there was sufficient cache pressure, entry being
accessed may be overwritten by another thread, resulting in a data
race.
We now make a thread local copy of the data, before releasing the
lock. If we end up supporting UNW_CACHE_PER_THREAD properly
in the future, this memcpy should be unnecessary.
Greetings,
Attached patch is rather on the obvious side: setting caching policy and
than doing nothing is pointless; we'd better acutally test that it works!
Tested on Linux/x86_64.
Thanks,
--
Paul Pluzhnikov
Greetings,
Attached patch gets rid of additional unnecessary branch (rs_get_cache
can not return NULL unless caching_policy is UNW_CACHE_NONE), gets rid of
goto's, and makes apply_reg_state (major CPU consumer) execute with cache
lock not held (before the patch, apply_reg_state was called with lock held
for newly-inserted entries, but not for found-in-cache entries).
Tested on Linux/x86_64 with no regressions.
Thanks,
--
Paul Pluzhnikov
Greetings,
Attached patch is rather on the obvious side:
- rs1 can't be NULL since it's assigned on previous line
- rs_new never returns NULL, and if it ever did, we'd crash on memcpy that
preceeds the NULL check.
Tested on Linux/x86_64 with no regressions.
Thanks,
--
Paul Pluzhnikov
