On Mon, Jul 6, 2015 at 1:38 PM, Paul Durrant <paul.durr...@citrix.com> wrote: >> -----Original Message----- >> From: dunl...@gmail.com [mailto:dunl...@gmail.com] On Behalf Of >> George Dunlap >> Sent: 06 July 2015 13:36 >> To: Yu Zhang >> Cc: xen-devel@lists.xen.org; Keir (Xen.org); Jan Beulich; Andrew Cooper; >> Paul Durrant; Kevin Tian; zhiyuan...@intel.com >> Subject: Re: [Xen-devel] [PATCH v2 1/2] Resize the MAX_NR_IO_RANGES for >> ioreq server >> >> On Mon, Jul 6, 2015 at 7:25 AM, Yu Zhang <yu.c.zh...@linux.intel.com> >> wrote: >> > MAX_NR_IO_RANGES is used by ioreq server as the maximum >> > number of discrete ranges to be tracked. This patch changes >> > its value to 8k, so that more ranges can be tracked on next >> > generation of Intel platforms in XenGT. Future patches can >> > extend the limit to be toolstack tunable, and MAX_NR_IO_RANGES >> > can serve as a default limit. >> > >> > Signed-off-by: Yu Zhang <yu.c.zh...@linux.intel.com> >> >> I said this at the Hackathon, and I'll say it here: I think this is >> the wrong approach. >> >> The problem here is not that you don't have enough memory ranges. The >> problem is that you are not tracking memory ranges, but individual >> pages. >> >> You need to make a new interface that allows you to tag individual >> gfns as p2m_mmio_write_dm, and then allow one ioreq server to get >> notifications for all such writes. >> > > I think that is conflating things. It's quite conceivable that more than one > ioreq server will handle write_dm pages. If we had enough types to have two > page types per server then I'd agree with you, but we don't.
What's conflating things is using an interface designed for *device memory ranges* to instead *track writes to gfns*. Fundamentally the reason you have this explosion of "device memory ranges" is that what you're tracking isn't device memory, and it isn't a range. If your umbrella isn't very good at hammering in nails, the solution is to go get a hammer, not to add steel reinforcement to your umbrella. My suggestion is, short-term, to simply allow the first ioreq server to register for write_dm notifications to get notifications, and return an error if a second one tries to do so. If it becomes important for a single domain to have two ioreq servers that need this functionality, then we can come up with an internal Xen structure, *designed for gfns*, to track this. My suspicion is that it will never be needed. -George _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
