On 05/27/2009 04:36 AM, FUJITA Tomonori wrote: > On Tue, 26 May 2009 19:05:05 +0300 > Boaz Harrosh <bharrosh@xxxxxxxxxxx> wrote: > >> On 05/26/2009 06:31 PM, FUJITA Tomonori wrote: >>> Can we just fix some drivers not to do the DMA with the sense buffer in >>> scsi_cmnd? IIRC, there are only five or six drivers that do such. >> This is not so. >> All drivers that go through scsi_eh_prep_cmnd() will eventually DMA through >> the regular read path. Including all the drivers that do nothing and let >> scsi-ml do the REQUEST_SENSE >> >> Actually I have exact numbers, from the last time I did all that > > Hmm, we discussed this before, I think. > Sure we did I sent these patches. to summarize, 3 types of drivers: 1. Only memcpy into sense_buffer - 60% 2. Use scsi_eh_prep_cmnd and DMA read into sense. 2.1 Do nothing and scsi-ml does scsi_eh_prep_cmnd - 30% 3. Prepare DMA descriptors for sense_buffer before execution - 10% > scsi-ml uses scsi_eh_prep_cmnd only via scsi_send_eh_cmnd(). There are > some users of scsi_send_eh_cmnd in scsi-ml but only scsi_request_sense > does the DMA in the sense_buffer of scsi_cmnd. > Also drivers use scsi_eh_prep_cmnd at interrupt time and proceed to DMA into the sense_buffer. > Only scsi_error_handler() uses scsi_request_sense() and > scsi_send_eh_cmnd() works synchronously. So scsi-ml can easily avoid > the the DMA in the sense_buffer of scsi_cmnd if we have one sense > buffer per scsi_host. Not so. As James explained then, once you have a CHECK_CONDITION return, the Q-per-host is frozen, yes. But as soon as you send the REQUEST_SENSE the target Q is unfrozen again and all in-flight commands can error, much before the REQUEST_SENSE returns. Boaz -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
