Messages in this thread | | | From | Kevin Corry <> | Subject | Re: [PATCH] dm.c - device-mapper I/O path fixes | Date | Wed, 11 Dec 2002 08:06:00 -0600 |
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On Wednesday 11 December 2002 13:24, Denis Vlasenko wrote: > On 11 December 2002 12:18, Joe Thornber wrote: > > On Wed, Dec 11, 2002 at 07:16:53AM -0600, Kevin Corry wrote: > > > However, it might be a good idea to consider how bio's keep track > > > of errors. When a bio is created, it is marked UPTODATE. Then, if > > > any part of a bio takes an error, the UPTODATE flag is turned off. > > > When the whole bio completes, if the UPTODATE flag is still on, > > > there were no errors during the i/o. Perhaps the "error" field in > > > "struct dm_io" could be modified to use this method of error > > > tracking? Then we could change dec_pending() to be something like: > > > > > > if (error) > > > clear_bit(DM_IO_UPTODATE, &io->error); > > > > > > with a "set_bit(DM_IO_UPTODATE, &ci.io->error);" in __bio_split(). > > > > The problem with this is you don't keep track of the specific error > > to later pass to bio_endio(io->bio...). I guess it all comes down to > > just how expensive that spin lock is; and since locking only occurs > > when there's an error I'm happy with things as they are. > > lock(); > a = b; > unlock(); > > Store of ints is atomic anyway. You need locking if a is a larger entity, > say, a struct.
Storing an int is *not* atomic unless it is declared as atomic_t and you use the appropriate macros (see include/asm-*/atomic.h). Remember, we are talking about a field in a data structure that can be accessed from multiple threads on multiple CPUs.
-- Kevin Corry corryk@us.ibm.com http://evms.sourceforge.net/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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