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rms: add a comment explaining performance deficiencies of write locking

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This commit is contained in:
Mateusz Guzik 2020-08-04 19:52:16 +00:00
parent d6502e7c67
commit 3211e783e3
1 changed files with 4 additions and 0 deletions
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sys/kern/kern_rmlock.c
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@ -872,6 +872,10 @@ db_show_rm(const struct lock_object *lock)
* Neither rms_rlock nor rms_runlock use fences. Instead compiler barriers are * Neither rms_rlock nor rms_runlock use fences. Instead compiler barriers are
* inserted to prevert reordering of generated code. Execution ordering is * inserted to prevert reordering of generated code. Execution ordering is
* provided with the use of an IPI handler. * provided with the use of an IPI handler.
*
* No attempt is made to track which CPUs read locked at least once,
* consequently write locking sends IPIs to all of them. This will become a
* problem at some point. The easiest way to lessen it is to provide a bitmamp.
*/ */
void void