On Wed, 27 May 2009 10:54:41 +0300 Boaz Harrosh <bharrosh@xxxxxxxxxxx> wrote: > 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. Hmm, I'm not sure what you mean. Why is 'all in-flight commands can error' a problem? The sense_buffer per host is used by only scsi_eh kernel thread. -- 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
