On 05/26/2009 07:12 PM, Boaz Harrosh wrote: > On 05/26/2009 05:47 PM, James Bottomley wrote: >> There are several other approaches: >> >> 1. Keep the sense buffer packed in the command but disallow DMA to >> it, which fixes all the alignment problems. Then we supply a >> set of rotating DMA buffers to drivers which need to do the DMA >> (which isn't the majority). > > This one is not possible because it is scsi-ml in majority of cases that > does the DMA request through scsi_eh_prep_cmnd() and a regular read. > The drivers don't even know anything about it. > I retract that no, yes and scsi-ml is one more possible client of the "rotating DMA buffers" >> 2. Sense is a comparative rarity, so us a more compact pooling >> scheme and discard sense for reuse as soon as we know it's not >> used (as in at softirq time when there's no sense collected). >> > > This is the way to go for sure. And only on ARCHs with none-coherent-cache > all the good ARCHs can just use embedded sense just fine. > >> I'd need a little more clarity on the actual size of the problem before >> making any choices. >> >> The other thing to bear in mind is that two allocations of M and N might >> be more costly than a single allocation of N+M; however, an allocation >> of M+N+extra can end up more costly if the extra causes more page >> reclaim before we get an actual command. >> >> James >> > Boaz > -- > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
