Russ Anderson (on Tue, 11 Mar 2008 16:22:21 -0500) wrote: >On Tue, Mar 11, 2008 at 03:07:20PM +0100, Zoltan Menyhart wrote: >> I still don't see any need for many buffers. > >In testing, I found one of the records getting dropped in salinfo.c >at the comment "saved record changed by mca.c since interrupt, discard it". >That code was not added by your patch, but is something that >impacts logging. A record getting dropped at that point indicates a race between salinfo.c and mca.c. salinfo.c is running under spin_lock_irqsave which is normally safe, but mca.c can be driven at any time and it completely ignores spin_lock_irqsave. mca.c grabs the next free buffer in the circular list and overwrites that buffer. The record id check detects that mca.c has overwritten this buffer while salinfo.c was processing it and retries the extraction of the record to user space. By definition whatever record was originally in the buffer has now been lost. Was the lost record of any use? No way of telling. The only way to avoid that loss is to increase the number of buffers. Any repeated sequence of recoverable MCA events will result in some loss of data, no matter how many buffers you allocate, simply because MCA processing has a higher priority than user space processing. -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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