On Tue, Sep 20, 2022 at 08:47:20PM -0400, Peter Xu wrote:
> On Tue, Sep 20, 2022 at 06:52:27PM -0400, Peter Xu wrote:
> > With the new code to send pages in rp-return thread, there's little help to
> > keep lots of the old code on maintaining the preempt state in migration
> > thread, because the new way should always be faster..
> >
> > Then if we'll always send pages in the rp-return thread anyway, we don't
> > need those logic to maintain preempt state anymore because now we serialize
> > things using the mutex directly instead of using those fields.
> >
> > It's very unfortunate to have those code for a short period, but that's
> > still one intermediate step that we noticed the next bottleneck on the
> > migration thread. Now what we can do best is to drop unnecessary code as
> > long as the new code is stable to reduce the burden. It's actually a good
> > thing because the new "sending page in rp-return thread" model is (IMHO)
> > even cleaner and with better performance.
> >
> > Remove the old code that was responsible for maintaining preempt states, at
> > the meantime also remove x-postcopy-preempt-break-huge parameter because
> > with concurrent sender threads we don't really need to break-huge anymore.
> >
> > Signed-off-by: Peter Xu <pet...@redhat.com>
> > ---
> > migration/migration.c | 2 -
> > migration/ram.c | 258 +-----------------------------------------
> > 2 files changed, 3 insertions(+), 257 deletions(-)
> >
> > diff --git a/migration/migration.c b/migration/migration.c
> > index fae8fd378b..698fd94591 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -4399,8 +4399,6 @@ static Property migration_properties[] = {
> > DEFINE_PROP_SIZE("announce-step", MigrationState,
> > parameters.announce_step,
> > DEFAULT_MIGRATE_ANNOUNCE_STEP),
> > - DEFINE_PROP_BOOL("x-postcopy-preempt-break-huge", MigrationState,
> > - postcopy_preempt_break_huge, true),
>
> Forgot to drop the variable altogether:
>
> diff --git a/migration/migration.h b/migration/migration.h
> index cdad8aceaa..ae4ffd3454 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -340,13 +340,6 @@ struct MigrationState {
> bool send_configuration;
> /* Whether we send section footer during migration */
> bool send_section_footer;
> - /*
> - * Whether we allow break sending huge pages when postcopy preempt is
> - * enabled. When disabled, we won't interrupt precopy within sending a
> - * host huge page, which is the old behavior of vanilla postcopy.
> - * NOTE: this parameter is ignored if postcopy preempt is not enabled.
> - */
> - bool postcopy_preempt_break_huge;
>
> /* Needed by postcopy-pause state */
> QemuSemaphore postcopy_pause_sem;
>
> Will squash this in in next version.
Two more varialbes to drop, as attached..
--
Peter Xu
>From b3308e34398e21c19bd36ec21aae9c7f9f623d75 Mon Sep 17 00:00:00 2001
From: Peter Xu <pet...@redhat.com>
Date: Wed, 21 Sep 2022 09:51:55 -0400
Subject: [PATCH] fixup! migration: Remove old preempt code around state
maintainance
Content-type: text/plain
Signed-off-by: Peter Xu <pet...@redhat.com>
---
migration/ram.c | 33 ---------------------------------
1 file changed, 33 deletions(-)
diff --git a/migration/ram.c b/migration/ram.c
index 03bf2324ab..2599eee070 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -97,28 +97,6 @@ struct PageSearchStatus {
unsigned long page;
/* Set once we wrap around */
bool complete_round;
- /*
- * [POSTCOPY-ONLY] Whether current page is explicitly requested by
- * postcopy. When set, the request is "urgent" because the dest QEMU
- * threads are waiting for us.
- */
- bool postcopy_requested;
- /*
- * [POSTCOPY-ONLY] The target channel to use to send current page.
- *
- * Note: This may _not_ match with the value in postcopy_requested
- * above. Let's imagine the case where the postcopy request is exactly
- * the page that we're sending in progress during precopy. In this case
- * we'll have postcopy_requested set to true but the target channel
- * will be the precopy channel (so that we don't split brain on that
- * specific page since the precopy channel already contains partial of
- * that page data).
- *
- * Besides that specific use case, postcopy_target_channel should
- * always be equal to postcopy_requested, because by default we send
- * postcopy pages via postcopy preempt channel.
- */
- bool postcopy_target_channel;
/* Whether we're sending a host page */
bool host_page_sending;
/* The start/end of current host page. Invalid if
host_page_sending==false */
@@ -1573,13 +1551,6 @@ retry:
*/
static bool find_dirty_block(RAMState *rs, PageSearchStatus *pss, bool *again)
{
- /*
- * This is not a postcopy requested page, mark it "not urgent", and use
- * precopy channel to send it.
- */
- pss->postcopy_requested = false;
- pss->postcopy_target_channel = RAM_CHANNEL_PRECOPY;
-
/* Update pss->page for the next dirty bit in ramblock */
pss_find_next_dirty(pss);
@@ -2091,9 +2062,6 @@ static bool get_queued_page(RAMState *rs,
PageSearchStatus *pss)
* really rare.
*/
pss->complete_round = false;
- /* Mark it an urgent request, meanwhile using POSTCOPY channel */
- pss->postcopy_requested = true;
- pss->postcopy_target_channel = RAM_CHANNEL_POSTCOPY;
}
return !!block;
@@ -2190,7 +2158,6 @@ int ram_save_queue_pages(const char *rbname, ram_addr_t
start, ram_addr_t len)
* we should be the only one who operates on the qemufile
*/
pss->pss_channel = migrate_get_current()->postcopy_qemufile_src;
- pss->postcopy_requested = true;
assert(pss->pss_channel);
/*
--
2.32.0
