migration/multifd: cache channel count in multifd_send_sync_main
multifd_send_sync_main() is called once per RAM synchronization round during live migration. It iterates over all multifd channels twice (signal loop + wait loop), calling migrate_multifd_channels() independently in each loop header. Cache migrate_multifd_channels() in a local thread_count variable at function entry, matching the pattern already used in multifd_send_setup() and multifd_recv_setup(). This eliminates 2 redundant config lookups per sync call. Signed-off-by: Bin Guo <guobin@linux.alibaba.com> Reviewed-by: Fabiano Rosas <farosas@suse.de> Link: https://lore.kernel.org/r/20260518110112.21395-9-guobin@linux.alibaba.com Signed-off-by: Peter Xu <peterx@redhat.com>
Bin Guo committed
May 18, 2026 at 19:01 UTC
ba9264240073c2bc4b0c1b3c1e65668122fb8f66
1 file changed
+4
-2
migration/multifd.c
+4
-2
@@ -611,13 +611,15 @@ static int multifd_zero_copy_flush(QIOChannel *c)
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int multifd_send_sync_main(MultiFDSyncReq req)
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{
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int i;
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+ int thread_count;
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bool flush_zero_copy;
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assert(req != MULTIFD_SYNC_NONE);
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+ thread_count = migrate_multifd_channels();
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flush_zero_copy = migrate_zero_copy_send();
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- for (i = 0; i < migrate_multifd_channels(); i++) {
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+ for (i = 0; i < thread_count; i++) {
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MultiFDSendParams *p = &multifd_send_state->params[i];
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if (multifd_send_should_exit()) {
@@ -634,7 +636,7 @@ int multifd_send_sync_main(MultiFDSyncReq req)
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qatomic_set(&p->pending_sync, req);
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qemu_sem_post(&p->sem);
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}
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- for (i = 0; i < migrate_multifd_channels(); i++) {
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+ for (i = 0; i < thread_count; i++) {
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MultiFDSendParams *p = &multifd_send_state->params[i];
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if (multifd_send_should_exit()) {