Messages in this thread | | | From | Ingo Molnar <> | Date | Wed, 6 May 2015 10:27:59 +0200 | Subject | Re: [PATCH] x86: skip delays during SMP initialization similar to Xen |
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* Jan H. Schönherr <jschoenh@amazon.de> wrote:
> Remove the per-CPU delays during SMP initialization, which seems to be > possible on newer architectures with an x2APIC. > > Xen does this since 2011. In fact, this commit is basically a > combination of the following Xen commits. The first removes the delays, > the second fixes an issue with the removal: > > commit 68fce206f6dba9981e8322269db49692c95ce250 > Author: Tim Deegan <Tim.Deegan@citrix.com> > Date: Tue Jul 19 14:13:01 2011 +0100 > > x86: Remove timeouts from INIT-SIPI-SIPI sequence when using x2apic. > > Some of the timeouts are pointless since they're waiting for the ICR > to ack the IPI delivery and that doesn't happen on x2apic. > The others should be benign (and are suggested in the SDM) but > removing them makes AP bringup much more reliable on some test boxes. > > Signed-off-by: Tim Deegan <Tim.Deegan@citrix.com> > > commit f12ee533150761df5a7099c83f2a5fa6c07d1187 > Author: Gang Wei <gang.wei@intel.com> > Date: Thu Dec 29 10:07:54 2011 +0000 > > X86: Add a delay between INIT & SIPIs for tboot AP bring-up in X2APIC case > > Without this delay, Xen could not bring APs up while working with > TXT/tboot, because tboot needs some time in APs to handle INIT before > becoming ready for receiving SIPIs (this delay was removed as part of > c/s 23724 by Tim Deegan). > > Signed-off-by: Gang Wei <gang.wei@intel.com> > Acked-by: Keir Fraser <keir@xen.org> > Acked-by: Tim Deegan <tim@xen.org> > Committed-by: Tim Deegan <tim@xen.org> > > Signed-off-by: Jan H. Schönherr <jschoenh@amazon.de> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: H. Peter Anvin <hpa@zytor.com> > Cc: Tim Deegan <tim@xen.org> > Cc: Gang Wei <gang.wei@intel.com> > --- > arch/x86/kernel/smpboot.c | 61 +++++++++++++++++++++++++++++------------------ > 1 file changed, 38 insertions(+), 23 deletions(-) > > This patch is against Linux 4.1-rc1.
So I really like this, as it nicely side-steps the 'when should we do the legacy delays' issue by flagging on x2apic support.
If anyone has objections, please holler.
Thanks,
Ingo
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