* Jan H. Schönherr <[email protected]> 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 <[email protected]>
> 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 <[email protected]>
>
> commit f12ee533150761df5a7099c83f2a5fa6c07d1187
> Author: Gang Wei <[email protected]>
> 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 <[email protected]>
> Acked-by: Keir Fraser <[email protected]>
> Acked-by: Tim Deegan <[email protected]>
> Committed-by: Tim Deegan <[email protected]>
>
> Signed-off-by: Jan H. Schönherr <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: H. Peter Anvin <[email protected]>
> Cc: Tim Deegan <[email protected]>
> Cc: Gang Wei <[email protected]>
> ---
> 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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