On Fri, Dec 19 2008, Vladislav Bolkhovitin wrote: > David M. Lloyd, on 12/18/2008 09:43 PM wrote: > >On 12/18/2008 12:35 PM, Vladislav Bolkhovitin wrote: > >>An iSCSI target driver iSCSI-SCST was a part of the patchset > >>(http://lkml.org/lkml/2008/12/10/293). For it a nice optimization to > >>have TCP zero-copy transmit of user space data was implemented. Patch, > >>implementing this optimization was also sent in the patchset, see > >>http://lkml.org/lkml/2008/12/10/296. > > > >I'm probably ignorant of about 90% of the context here, but isn't this the > >sort of problem that was supposed to have been solved by vmsplice(2)? > > No, vmsplice can't help here. ISCSI-SCST is a kernel space driver. But, > even if it was a user space driver, vmsplice wouldn't change anything > much. It doesn't have a possibility for a user to know, when > transmission of the data finished. So, it is intended to be used as: > vmsplice() buffer -> munmap() the buffer -> mmap() new buffer -> > vmsplice() it. But on the mmap() stage kernel has to zero all the newly > mapped pages and zeroing memory isn't much faster, than copying it. > Hence, there would be no considerable performance increase. vmsplice() isn't the right choice, but splice() very well could be. You could easily use splice internally as well. The vmsplice() part sort-of applies in the sense that you want to fill pages into a pipe, which is essentially what vmsplice() does. You'd need some helper to do that. And the ack-on-xmit-done bits is something that splice-to-socket needs anyway, so I think it'd be quite a suitable choice for this. -- 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
