On 13/02/2023 20:53, David Woodhouse wrote:
On 13 February 2023 21:43:13 CET, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
On Thu, Feb 09 2023 at 15:41, Usama Arif wrote:
From: David Woodhouse <dwmw@xxxxxxxxxxxx>
The toplogy update is performed by the AP via smp_callin() after the BSP
has called do_wait_cpu_initialized(), setting the AP's bit in
cpu_callout_mask to allow it to proceed.
In preparation to enable further parallelism of AP bringup, add locking to
serialize the update even if multiple APs are (in future) permitted to
proceed through the next stages of bringup in parallel.
This one is also only relevant for further parallelisation, right?
I believe so, yes. But it's low-hanging fruit and might as well go in now.
Yes, only needed if we parallelize further, i.e. after
do_wait_cpu_initialized. As David said, its a simple enough and easy
patch, but its not needed for parallelizing INIT/SIPI.
I tested Davids' part2 branch
(https://git.infradead.org/users/dwmw2/linux.git/shortlog/refs/heads/parallel-6.2-rc7)
again just to be sure, and the only commit that makes a significant
difference in smpboot time on top of part1 (this series) is reusing
timer calibration (100ms to 34ms).
Parallelizing do_wait_cpu_initialized didn't significantly improve
smpboot time (only reduced to 31ms on average of 4 runs so maybe within
the margin of error?), so I think its better to move this patch into its
own series with any further parallelization only if it shows a further
improvement in smpboot time?
Thanks,
Usama
