> -----Original Message----- > From: Julien Grall <jul...@xen.org> > Sent: 24 April 2020 11:35 > To: p...@xen.org; 'Jan Beulich' <jbeul...@suse.com>; > xen-devel@lists.xenproject.org > Cc: 'Andrew Cooper' <andrew.coop...@citrix.com>; 'George Dunlap' > <george.dun...@citrix.com>; 'Ian > Jackson' <ian.jack...@eu.citrix.com>; 'Stefano Stabellini' > <sstabell...@kernel.org>; 'Wei Liu' > <w...@xen.org> > Subject: Re: [PATCH 0/3] xenoprof: XSA-313 follow-up > > Hi Paul, > > On 20/04/2020 16:01, Paul Durrant wrote: > >> -----Original Message----- > >> From: Julien Grall <jul...@xen.org> > >> Sent: 20 April 2020 15:15 > >> To: p...@xen.org; 'Jan Beulich' <jbeul...@suse.com>; > >> xen-devel@lists.xenproject.org > >> Cc: 'Andrew Cooper' <andrew.coop...@citrix.com>; 'George Dunlap' > >> <george.dun...@citrix.com>; 'Ian > >> Jackson' <ian.jack...@eu.citrix.com>; 'Stefano Stabellini' > >> <sstabell...@kernel.org>; 'Wei Liu' > >> <w...@xen.org> > >> Subject: Re: [PATCH 0/3] xenoprof: XSA-313 follow-up > >> > >> Hi Paul, > >> > >> On 15/04/2020 09:50, Paul Durrant wrote: > >>>> -----Original Message----- > >>>> From: Jan Beulich <jbeul...@suse.com> > >>>> Sent: 15 April 2020 09:45 > >>>> To: xen-devel@lists.xenproject.org > >>>> Cc: Andrew Cooper <andrew.coop...@citrix.com>; George Dunlap > >>>> <george.dun...@citrix.com>; Ian > >> Jackson > >>>> <ian.jack...@eu.citrix.com>; Julien Grall <jul...@xen.org>; Stefano > >>>> Stabellini > >>>> <sstabell...@kernel.org>; Wei Liu <w...@xen.org>; Paul Durrant > >>>> <p...@xen.org> > >>>> Subject: [PATCH 0/3] xenoprof: XSA-313 follow-up > >>>> > >>>> Patch 1 was considered to become part of the XSA, but it was then > >>>> decided against. The other two are a little bit of cleanup, albeit > >>>> there's certainly far more room for tidying. Yet then again Paul, > >>>> in his mail from Mar 13, was asking whether we shouldn't drop > >>>> xenoprof altogether, at which point cleaning up the code would be > >>>> wasted effort. > >>>> > >>> > >>> That's still my opinion. This is a large chunk of (only passively > >>> maintained) code which I think > is > >> of very limited value (since it relates to an old tool, and it only works > >> for PV domains). > >> > >> While there are no active user we are aware of, this is an example on > >> how to implement a profiler backend with Xen. So I would agree with > >> Andrew here. > >> > >> IIRC, the reason behind your request is it makes difficult for your > >> xenheap work. Am I correct? If so, do you have a thread explaining the > >> issues? > > > > After shared info and grant table, it is the only other occurrence of a > > xenheap page shared with a > non-system domain. Also, it cannot be trivially replaced with an 'extra' > domheap page because its > assignment changes. Thus a whole bunch of cleanup work that I was hoping to > do (largely in > domain_relinquish_resources and free_domheap_pages) is either ruled out, or > would have to special-case > this type of page. > > My knowledge of xenoprof is very limited, so I might be wrong. > > From my understanding, a buffer can only be shared between two domains: > - When in passive mode, the buffer will be shared with the primary > profiler (always the hwdom per the check in xenoprof_op_init()). > - When in active mode, the buffer will be shared with the domain > requesting to be profiled. > > Would it be possible to consider to have a separate buffer for the > passive mode and active mode?
I think that may well work, yes. > > > Also, I am unconvinced that PV guests are sufficiently common these days > > (apart from dom0) that > profiling them is of any real use. > > Even an HVM guest can't profile itself, I think it would be useful to > have dom0 to profile an HVM guest. Are you suggesting this doesn't work? > No. That may work for a PV dom0; I'll have to try it. So, yes, passive profiling may indeed still have value. Paul
