From: Wei Liu <wl@xen.org>
To: "Xia, Hongyan" <hongyxia@amazon.com>
Cc: "wl@xen.org" <wl@xen.org>,
"andrew.cooper3@citrix.com" <andrew.cooper3@citrix.com>,
"Grall, Julien" <jgrall@amazon.com>,
"jbeulich@suse.com" <jbeulich@suse.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
"roger.pau@citrix.com" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH v2] x86/domain_page: implement pure per-vCPU mapping infrastructure
Date: Fri, 21 Feb 2020 14:39:18 +0000 [thread overview]
Message-ID: <20200221143918.o32sq4nx3xiqc7py@debian> (raw)
In-Reply-To: <2326943257e6f04bc9a858ef5667295651395c85.camel@amazon.com>
On Fri, Feb 21, 2020 at 12:52:07PM +0000, Xia, Hongyan wrote:
> On Fri, 2020-02-21 at 11:50 +0000, Wei Liu wrote:
> > On Thu, Feb 06, 2020 at 06:58:23PM +0000, Hongyan Xia wrote:
> > > ...
> > >
> > > Benchmarks
> > > (baseline uses direct map instead of the mapcache in
> > > map_domain_page,
> > > old is the existing mapcache and new is after this patch):
> > >
> > > Geekbench on a 32-vCPU guest,
> > >
> > > performance drop old new
> > > single core 0.04% 0.18%
> >
> > Do you know why the new mapcache has more overhead than the old one
> > in
> > the single core case?
>
> To be honest I think this is within noise territory. The benchmarks
> were run 5 times, I can average over even more runs to confirm.
I would think so too, because there shouldn't be contention in single
vcpu case. I was a bit surprised to see the numbers.
[...]
> > > + rc = create_perdomain_mapping(d, MAPCACHE_VIRT_START,
> > > ents,
> > > NIL(l1_pgentry_t *),
> > > NULL);
> > >
> > > - /* Populate bit maps. */
> > > - if ( !rc )
> > > - rc = create_perdomain_mapping(d, (unsigned
> > > long)dcache->inuse,
> > > - nr, NULL, NIL(struct
> > > page_info *));
> > > - if ( !rc )
> > > - rc = create_perdomain_mapping(d, (unsigned
> > > long)dcache->garbage,
> > > - nr, NULL, NIL(struct
> > > page_info *));
> > > -
> > > if ( rc )
> > > return rc;
> > >
> > > dcache->entries = ents;
> >
> > Given that:
> >
> > 1. mapcache_domain is now a structure with only one member.
> > 2. ents is a constant throughout domain's lifecycle.
> >
> > You can replace mapcache_domain with a boolean --
> > mapcache_mapping_populated (?) in arch.pv.
> >
> > If I'm not mistaken, the size of the mapping is derived from the vcpu
I really meant "isn't" here.
> > being initialised, so a further improvement is to lift the mapping
> > creation out of mapcache_vcpu_init.
>
> But you can just XEN_DOMCTL_max_vcpus on a running domain to increase
> its max_vcpus count, so that ents is not constant?
>
What Andrew said in his mail.
Wei.
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prev parent reply other threads:[~2020-02-21 14:39 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-06 18:58 [Xen-devel] [PATCH v2] x86/domain_page: implement pure per-vCPU mapping infrastructure Hongyan Xia
2020-02-21 11:50 ` Wei Liu
2020-02-21 12:52 ` Xia, Hongyan
2020-02-21 13:02 ` Andrew Cooper
2020-02-21 14:40 ` Xia, Hongyan
2020-02-21 13:31 ` Jan Beulich
2020-02-21 14:36 ` Wei Liu
2020-02-21 14:55 ` Jan Beulich
2020-02-21 14:58 ` Wei Liu
2020-02-21 15:08 ` Jan Beulich
2020-02-21 14:52 ` Xia, Hongyan
2020-02-21 14:59 ` Jan Beulich
2020-02-21 14:39 ` Wei Liu [this message]
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