On Wed, May 30 2007, Andrew Patterson wrote: > On Wed, 2007-05-30 at 14:22 -0500, James Bottomley wrote: > > On Wed, 2007-05-30 at 21:11 +0200, Jens Axboe wrote: > > > > > > > > > There's no other solution than maintaining a cached request + command > > > > > > > > > for this. libata has a similar issue wrt error handling with ncq, we may > > > > > > > > > need a command in error handling to retrieve the log page. > > > > > > > > > > > > > > > > Actually, there is another solution: DV is careful only to be using a > > > > > > > > single command for its processes ... if we could use the eh command for > > > > > > > > this, then I think the problem would go away ... unfortunately, that's a > > > > > > > > bit more complex to achieve than it sounds. > > > > > > > > > > (btw this is not another solution, it's indeed the solution of keeping a > > > > > reserved request :-) > > > > > > > > > > > > That would be fine, the key is just to have such a reserved command. Is > > > > > > > there also a reserved request? > > > > > > > > > > > > Yes ... we clean out the failing command in error recovery and reuse it, > > > > > > so we know it has both a command and a request. > > > > > > > > > > Sounds a bit hackish, unless the failed command never needs to be > > > > > retried. > > > > > > > > Oh, it does. We clean it out, save the necessary on the stack and reuse > > > > it, then restore the data and send it for a retry. Up until a while ago > > > > it was what all the old_ fields were for in the SCSI command; now, after > > > > Christoph fixed it, we save them on the stack instead. > > > > > > I guess the scsi command doesn't need a whole lot of saved state, but > > > the request does. > > > > Well, we're careful never to let the block layer see it again. We have > > a special injection point scsi_send_eh_cmnd() for this. On the other > > hand ... supposing we were to push it back on the block queue for a > > resend, what would we need to save? It's fully prepared and set up as > > special because of the attached command, so I'm not sure there would be > > anything, as long as we don't let it go into the normal block completion > > paths ... I'm just wondering if we can get rid of the special injection > > path. > > > > James > > > > > > Rather than reusing a request, can we just somehow signal the block > layer to let this command exceed the current nr_request limit and go on > through? This would be similar to the ioc_batching mechanism currently > in use. And if there's no more memory left, what do you do? -- Jens Axboe - 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
