>>> On 30.06.14 at 13:18, <JGross@xxxxxxxx> wrote: > On 06/30/2014 01:02 PM, Jan Beulich wrote: >>>>> On 27.06.14 at 19:11, <konrad.wilk@xxxxxxxxxx> wrote: >>> On Fri, Jun 27, 2014 at 04:34:33PM +0200, jgross@xxxxxxxx wrote: >>>> +/* >>>> + * Maximum scatter/gather segments per request. >>>> + * >>>> + * Considering balance between allocating at least 16 "vscsiif_request" >>>> + * structures on one page (4096 bytes) and the number of scatter/gather >>>> + * elements needed, we decided to use 26 as a magic number. >>>> + */ >>>> +#define VSCSIIF_SG_TABLESIZE 26 >>>> + >>>> +/* >>>> + * based on Linux kernel 2.6.18 >>> >>> This being a bit more .. new, - do these sizes make sense anymore? >>> Should they be extended a bit? Or have support for using the >>> old ones (as default) and then negotiate new sizes with the kernel? >>> (If of course there is a difference?) >> >> As Jürgen already said (and as you should have noticed yourself) - >> this is an interface definition that we can't just change. Negotiation >> of larger counts is an option, which is what VSCSIIF_ACT_SCSI_SG_PRESET >> is intended for (the implementation of which isn't part of this patchset >> afaics, but could be made available on top of it). > > I don't think this is the proper way to handle larger SG lists. The > VSCSIIF_ACT_SCSI_SG_PRESET option would just bump the maximum length > up to 31 (currently 26). Or was it thought to be incremental (multiple > presets for one request)? Yes, that's how it's to be used. See xen-vscsi-large-requests.patch it the newer of our trees. > I'd rather add a way to specify SG lists > residing in an own (granted) page (or even multiple pages). This would > allow 512*26 SG entries without having to change the request structure. > The capability to handle this feature could be indicated via xenstore. And yes, considering the similar changes in blkif I agree that this would be the preferred method today. That patch, however, predates those blkif enhancements. Jan -- 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
