On Wed, Jan 14, 2015 at 9:13 AM, Shaohua Li <shli@xxxxxx> wrote: > On Wed, Jan 14, 2015 at 09:04:24AM -0800, Dan Williams wrote: >> On Wed, Jan 14, 2015 at 8:30 AM, Shaohua Li <shli@xxxxxx> wrote: >> >> > On Wed, Jan 14, 2015 at 12:08:26AM -0800, Dan Williams wrote: >> > > On Fri, Jan 9, 2015 at 2:12 PM, Shaohua Li <shli@xxxxxx> wrote: >> > > > On Fri, Jan 09, 2015 at 01:59:19PM -0800, Shaohua Li wrote: >> > > >> On Fri, Jan 09, 2015 at 04:43:07PM -0500, Tejun Heo wrote: >> > > >> > On Fri, Jan 09, 2015 at 10:15:29AM -0800, Shaohua Li wrote: >> > > >> > > Ping! >> > > >> > >> > > >> > I like the idea but it bothers me that we end up with two separate >> > > >> > ways of allocating command tags. Any chance the old one can be >> > > >> > removed? >> > > > >> > > > Oh, sorry, my reply truncated. >> > > > >> > > > So I checked with IPR driver guys, the ipr doesn't use ncq, so we can >> > > > always use sata tag 0, but not sure for libsas. >> > > > >> > > > Maybe Dan can answer if there is a way we can map SCSI tag to SATA tag. >> > > > >> > > >> > > For libsas or for ata drivers? For libsas, iirc, the internal libata >> > > tag is ignored and we use the scsi tag for the sas task For ata some >> > > drivers want round robin, but others appear to care about using the >> > > lowest available: >> > https://urldefense.proofpoint.com/v1/url?u=https://bugzilla.kernel.org/show_bug.cgi?id%3D87101&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=3RFlL12A7nwmLRXunVJq2g%3D%3D%0A&m=i5Fz0FbsOgTMAtXW2WeXro9juvX%2BRmkKOK%2Fnl5ZZWMw%3D%0A&s=b8747b79ff51a364a841dd8e2ff51814536fcd63eedb7ad8f1de68e6691e5e98 >> > . >> > > >> > > Is ata using it's own legacy tag ordering scheme getting in the way of >> > > other improvements? I'd just as soon recommend letting legacy dogs >> > > lie. In other words what do we gain by switching? >> > > >> > > I need to follow up on bz87101, seems I never reworked the patch as >> > > Tejun asked. However, I'm glad a fix like the one proposed in that >> > > report can be self-contained to libata and need not worry about >> > > supporting ata specific quirks in the block layer tag ordering scheme. >> > >> > Basically I'd like using block tag instead of an open coded tag >> > implementation in libata. The block tag implenmentation is more >> > sophisticated, and with blk-mq tag is built-in, so it's great to remove >> > tag implementation in libata. >> >> >> Is it great to remove? It's not clear what the cost of maintaining it is. >> How would you handle the case where some ata controllers want the lowest >> available tag vs others that want round robin. > > I added a flag to blk-tag/blk-mq tag to implement different tag > allocation strategy, for example, round robin and fifo. Right, but you seem to do it at the scsi_host level, if I'm not mistaken. Isn't that too high for ata quirks? >> > For sata, it's easy to do it. The problem >> > is sas, which implements its own scsi driver/tag. My question is if we >> > can map SCSI tag (of libsas) to ATA tag. So for example, the ipr sas >> > driver doesn't use NCQ, so we can always use ata tag 0 in libata for >> > ipr. I'm wondering if we can do some mapping in libsas too, so we can >> > completely delete the tag code in libata. >> > >> >> The problem with using the scsi tag for libsas is that the scsi_host may >> support 256 commands, but only 32 per ata device. Seems like a problem >> blk-mq has already solved (controller + per-endpoint tag queues), but I >> have not looked... > > This is exactly the issue I'm talking about. Is there a way to map the > 256 (scsi tag) to ata tag for libsas? Like I said, for ipr sas, I'll do > scsi tag -> ata tag 0, since it doesn't use NCQ for SATA. Is there > something similar or whatever for libsas? From search, ipr and libsas > are the only scsi drivers using libata. libsas uses the libata allocated tag for NCQ. libsas first asks libata to allocate a tag/qc for ncq, then it creates a sas_task and assigns the scsi tag. To use a generic allocator I assume you would need to flip that ordering to allocate the sas_task tag first and then use that plus another key to allocate a sub-tag for ata to use for NCQ. -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
