Thanks for your data. Seemly, those data is acceptable on OvmfXen. For this patch, Reviewed-by: Liming Gao <liming....@intel.com>
Thanks Liming > -----Original Message----- > From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Anthony PERARD > Sent: Tuesday, February 4, 2020 1:26 AM > To: Gao, Liming <liming....@intel.com> > Cc: Laszlo Ersek <ler...@redhat.com>; devel@edk2.groups.io; Kinney, Michael D > <michael.d.kin...@intel.com>; Ard Biesheuvel > <ard.biesheu...@linaro.org>; xen-de...@lists.xenproject.org; Justen, Jordan L > <jordan.l.jus...@intel.com>; Julien Grall > <jul...@xen.org>; Feng, Bob C <bob.c.f...@intel.com> > Subject: Re: [edk2-devel] [PATCH 2/5] MdePkg: Allow PcdFSBClock to by Dynamic > > On Mon, Feb 03, 2020 at 03:34:07PM +0000, Anthony PERARD wrote: > > On Mon, Feb 03, 2020 at 01:34:55AM +0000, Gao, Liming wrote: > > > Anthony: > > > This change is OK to me. But if this PCD is configured as Dynamic, its > > > value will be got from PCD service. This operation will take > some time and cause the inaccurate time delay. Have you measured its impact? > > > > No, I haven't. But I don't think it matter in a Xen guest, the APIC timer is > > emulated anyway, so reading from a register of the APIC is going to be > > slower than getting the value from the PCD services, I think. > > (Hopefully, I'm not too wrong.) > > > > But I'll give it at measuring the difference, it would be interesting to > > know. > > Now that I've given a try, having the value as Dynamic doesn't change > anything in a Xen guest. > > On my test machine, simply running GetPerformanceCounter (); takes > between 10000 ns and 20000 ns. Reading the dynamic value from PCD on the > other hand takes about 350ns. (10ns if it's static.) > > When I run NanoSecondDelay() with different values, I have: > - with static pcd: > 63894 ns to delay by 1 ns > 66611 ns to delay by 10 ns > 43927 ns to delay by 100 ns > 71367 ns to delay by 1000 ns > 55881 ns to delay by 10000 ns > 147716 ns to delay by 100000 ns > 1048335 ns to delay by 1000000 ns > 10041179 ns to delay by 10000000 ns > - with a dynamic pcd: > 40949 ns to delay by 1 ns > 84832 ns to delay by 10 ns > 82745 ns to delay by 100 ns > 59848 ns to delay by 1000 ns > 52647 ns to delay by 10000 ns > 137051 ns to delay by 100000 ns > 1042492 ns to delay by 1000000 ns > 10036306 ns to delay by 10000000 ns > > So, the kind of PCD used for PcdFSBClock on Xen (with OvmfXen) doesn't > really matter. > > Anyway, thanks for the feedback. > > -- > Anthony PERARD > > -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#53697): https://edk2.groups.io/g/devel/message/53697 Mute This Topic: https://groups.io/mt/70239981/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
