Re: [Qemu-devel] [PATCH v3] migration: always initial ram_counters for a new migration

[Wei Yang <richardw.yang@linux.intel.com>]

On Fri, Aug 02, 2019 at 06:18:41PM +0800, Ivan Ren wrote:
>From: Ivan Ren <ivanren@tencent.com>
>
>This patch fix a multifd migration bug in migration speed calculation, this
>problem can be reproduced as follows:
>1. start a vm and give a heavy memory write stress to prevent the vm be
>   successfully migrated to destination
>2. begin a migration with multifd
>3. migrate for a long time [actually, this can be measured by transferred bytes]
>4. migrate cancel
>5. begin a new migration with multifd, the migration will directly run into
>   migration_completion phase
>
>Reason as follows:
>
>Migration update bandwidth and s->threshold_size in function
>migration_update_counters after BUFFER_DELAY time:
>
>    current_bytes = migration_total_bytes(s);
>    transferred = current_bytes - s->iteration_initial_bytes;
>    time_spent = current_time - s->iteration_start_time;
>    bandwidth = (double)transferred / time_spent;
>    s->threshold_size = bandwidth * s->parameters.downtime_limit;
>
>In multifd migration, migration_total_bytes function return
>qemu_ftell(s->to_dst_file) + ram_counters.multifd_bytes.
>s->iteration_initial_bytes will be initialized to 0 at every new migration,
>but ram_counters is a global variable, and history migration data will be
>accumulated. So if the ram_counters.multifd_bytes is big enough, it may lead
>pending_size >= s->threshold_size become false in migration_iteration_run
>after the first migration_update_counters.
>
>Signed-off-by: Ivan Ren <ivanren@tencent.com>
>Reviewed-by: Juan Quintela <quintela@redhat.com>
>Suggested-by: Wei Yang <richardw.yang@linux.intel.com>
>---
>v2->v3:
>- fix the bug of update_iteration_initial_status function prototype
>

Code looks good. Have you verified on this version?

BTW, you didn't address the multifd count in this patch, right?


-- 
Wei Yang
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