Re: [PATCH v2 5/5] migration: Add tracepoints for downtime checkpoints

[Juan Quintela <quintela@redhat.com>]

Peter Xu <peterx@redhat.com> wrote:
> This patch is inspired by Joao Martin's patch here:
>
> https://lore.kernel.org/r/20230926161841.98464-1-joao.m.martins@oracle.com
>
> Add tracepoints for major downtime checkpoints on both src and dst.  They
> share the same tracepoint with a string showing its stage.
>
> Besides the checkpoints in the previous patch, this patch also added
> destination checkpoints.
>
> On src, we have these checkpoints added:
>
>   - src-downtime-start: right before vm stops on src
>   - src-vm-stopped: after vm is fully stopped
>   - src-iterable-saved: after all iterables saved (END sections)
>   - src-non-iterable-saved: after all non-iterable saved (FULL sections)
>   - src-downtime-stop: migration fully completed
>
> On dst, we have these checkpoints added:
>
>   - dst-precopy-loadvm-completes: after loadvm all done for precopy
>   - dst-precopy-bh-*: record BH steps to resume VM for precopy
>   - dst-postcopy-bh-*: record BH steps to resume VM for postcopy
>
> On dst side, we don't have a good way to trace total time consumed by
> iterable or non-iterable for now.  We can mark it by 1st time receiving a
> FULL / END section, but rather than that let's just rely on the other
> tracepoints added for vmstates to back up the information.
>
> With this patch, one can enable "vmstate_downtime*" tracepoints and it'll
> enable all tracepoints for downtime measurements necessary.
>
> Drop loadvm_postcopy_handle_run_bh() tracepoint alongside, because they
> service the same purpose, which was only for postcopy.  We then have
> unified prefix for all downtime relevant tracepoints.
>
> Co-developed-by: Joao Martins <joao.m.martins@oracle.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Juan Quintela <quintela@redhat.com>