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Re: [Qemu-devel] [PATCH 2/2] migration: not wait RDMA_CM_EVENT_DISCONNEC
From: |
858585 jemmy |
Subject: |
Re: [Qemu-devel] [PATCH 2/2] migration: not wait RDMA_CM_EVENT_DISCONNECTED event after rdma_disconnect |
Date: |
Tue, 22 May 2018 18:12:24 +0800 |
On Wed, May 16, 2018 at 9:13 PM, Dr. David Alan Gilbert
<address@hidden> wrote:
> * 858585 jemmy (address@hidden) wrote:
>
> <snip>
>
>> >> >> > I wonder why dereg_mr takes so long - I could understand if reg_mr
>> >> >> > took a long time, but why for dereg, that sounds like the easy side.
>> >> >>
>> >> >> I use perf collect the information when ibv_dereg_mr is invoked.
>> >> >>
>> >> >> - 9.95% client2 [kernel.kallsyms] [k] put_compound_page
>> >> >> `
>> >> >> - put_compound_page
>> >> >> - 98.45% put_page
>> >> >> __ib_umem_release
>> >> >> ib_umem_release
>> >> >> dereg_mr
>> >> >> mlx5_ib_dereg_mr
>> >> >> ib_dereg_mr
>> >> >> uverbs_free_mr
>> >> >> remove_commit_idr_uobject
>> >> >> _rdma_remove_commit_uobject
>> >> >> rdma_remove_commit_uobject
>> >> >> ib_uverbs_dereg_mr
>> >> >> ib_uverbs_write
>> >> >> vfs_write
>> >> >> sys_write
>> >> >> system_call_fastpath
>> >> >> __GI___libc_write
>> >> >> 0
>> >> >> + 1.55% __ib_umem_release
>> >> >> + 8.31% client2 [kernel.kallsyms] [k] compound_unlock_irqrestore
>> >> >> + 7.01% client2 [kernel.kallsyms] [k] page_waitqueue
>> >> >> + 7.00% client2 [kernel.kallsyms] [k] set_page_dirty
>> >> >> + 6.61% client2 [kernel.kallsyms] [k] unlock_page
>> >> >> + 6.33% client2 [kernel.kallsyms] [k] put_page_testzero
>> >> >> + 5.68% client2 [kernel.kallsyms] [k] set_page_dirty_lock
>> >> >> + 4.30% client2 [kernel.kallsyms] [k] __wake_up_bit
>> >> >> + 4.04% client2 [kernel.kallsyms] [k] free_pages_prepare
>> >> >> + 3.65% client2 [kernel.kallsyms] [k] release_pages
>> >> >> + 3.62% client2 [kernel.kallsyms] [k] arch_local_irq_save
>> >> >> + 3.35% client2 [kernel.kallsyms] [k] page_mapping
>> >> >> + 3.13% client2 [kernel.kallsyms] [k] get_pageblock_flags_group
>> >> >> + 3.09% client2 [kernel.kallsyms] [k] put_page
>> >> >>
>> >> >> the reason is __ib_umem_release will loop many times for each page.
>> >> >>
>> >> >> static void __ib_umem_release(struct ib_device *dev, struct ib_umem
>> >> >> *umem, int dirty)
>> >> >> {
>> >> >> struct scatterlist *sg;
>> >> >> struct page *page;
>> >> >> int i;
>> >> >>
>> >> >> if (umem->nmap > 0)
>> >> >> ib_dma_unmap_sg(dev, umem->sg_head.sgl,
>> >> >> umem->npages,
>> >> >> DMA_BIDIRECTIONAL);
>> >> >>
>> >> >> for_each_sg(umem->sg_head.sgl, sg, umem->npages, i) { <<
>> >> >> loop a lot of times for each page.here
>> >> >
>> >> > Why 'lot of times for each page'? I don't know this code at all, but
>> >> > I'd expected once per page?
>> >>
>> >> sorry, once per page, but a lot of page for a big size virtual machine.
>> >
>> > Ah OK; so yes it seems best if you can find a way to do the release in
>> > the migration thread then; still maybe this is something some
>> > of the kernel people could look at speeding up?
>>
>> The kernel code seem is not complex, and I have no idea how to speed up.
>
> Me neither; but I'll ask around.
>
>> >> >
>> >> > With your other kernel fix, does the problem of the missing
>> >> > RDMA_CM_EVENT_DISCONNECTED events go away?
>> >>
>> >> Yes, after kernel and qemu fixed, this issue never happens again.
>> >
>> > I'm confused; which qemu fix; my question was whether the kernel fix by
>> > itself fixed the problem of the missing event.
>>
>> this qemu fix:
>> migration: update index field when delete or qsort RDMALocalBlock
>
> OK good; so then we shouldn't need this 2/2 patch.
>
>> this issue also cause by some ram block is not released. but I do not
>> find the root cause.
>
> Hmm, we should try and track that down.
>
>> >
>> >> Do you think we should remove rdma_get_cm_event after rdma_disconnect?
>> >
>> > I don't think so; if 'rdma_disconnect' is supposed to generate the event
>> > I think we're supposed to wait for it to know that the disconnect is
>> > really complete.
>>
>> After move qemu_fclose to migration thread, it will not block the main
>> thread when wait
>> the disconnection event.
>
> I'm not sure about moving the fclose to the migration thread; it worries
> me with the interaction with cancel and other failures.
Bad news, I find the destination qemu also have this problem today.
when the precopy migration finished, the destination qemu main thread
process_incoming_migration_co will call qemu_fclose(f), and cause the
guest os hang for a while.
so I think it's better to solve this problem by rdma.c itself, not
change the migration.c code
when calling qemu_fclose.
we can create a separate thread in qemu_rdma_cleanup, and release the
resource in the
separate thread.
>
> Dave
>
>> >
>> > Dave
>> >
>> >>
>> >> >
>> >> > Dave
>> >> >
>> >> >> page = sg_page(sg);
>> >> >> if (umem->writable && dirty)
>> >> >> set_page_dirty_lock(page);
>> >> >> put_page(page);
>> >> >> }
>> >> >>
>> >> >> sg_free_table(&umem->sg_head);
>> >> >> return;
>> >> >> }
>> >> >>
>> >> >> >
>> >> >> > Dave
>> >> >> >
>> >> >> >
>> >> >> >> >
>> >> >> >> > Dave
>> >> >> >> >
>> >> >> >> >> >
>> >> >> >> >> >> Anyway, it should not invoke rdma_get_cm_event in main
>> >> >> >> >> >> thread, and the event channel
>> >> >> >> >> >> is also destroyed in qemu_rdma_cleanup.
>> >> >> >> >> >>
>> >> >> >> >> >> Signed-off-by: Lidong Chen <address@hidden>
>> >> >> >> >> >> ---
>> >> >> >> >> >> migration/rdma.c | 12 ++----------
>> >> >> >> >> >> migration/trace-events | 1 -
>> >> >> >> >> >> 2 files changed, 2 insertions(+), 11 deletions(-)
>> >> >> >> >> >>
>> >> >> >> >> >> diff --git a/migration/rdma.c b/migration/rdma.c
>> >> >> >> >> >> index 0dd4033..92e4d30 100644
>> >> >> >> >> >> --- a/migration/rdma.c
>> >> >> >> >> >> +++ b/migration/rdma.c
>> >> >> >> >> >> @@ -2275,8 +2275,7 @@ static int qemu_rdma_write(QEMUFile *f,
>> >> >> >> >> >> RDMAContext *rdma,
>> >> >> >> >> >>
>> >> >> >> >> >> static void qemu_rdma_cleanup(RDMAContext *rdma)
>> >> >> >> >> >> {
>> >> >> >> >> >> - struct rdma_cm_event *cm_event;
>> >> >> >> >> >> - int ret, idx;
>> >> >> >> >> >> + int idx;
>> >> >> >> >> >>
>> >> >> >> >> >> if (rdma->cm_id && rdma->connected) {
>> >> >> >> >> >> if ((rdma->error_state ||
>> >> >> >> >> >> @@ -2290,14 +2289,7 @@ static void
>> >> >> >> >> >> qemu_rdma_cleanup(RDMAContext *rdma)
>> >> >> >> >> >> qemu_rdma_post_send_control(rdma, NULL, &head);
>> >> >> >> >> >> }
>> >> >> >> >> >>
>> >> >> >> >> >> - ret = rdma_disconnect(rdma->cm_id);
>> >> >> >> >> >> - if (!ret) {
>> >> >> >> >> >> - trace_qemu_rdma_cleanup_waiting_for_disconnect();
>> >> >> >> >> >> - ret = rdma_get_cm_event(rdma->channel,
>> >> >> >> >> >> &cm_event);
>> >> >> >> >> >> - if (!ret) {
>> >> >> >> >> >> - rdma_ack_cm_event(cm_event);
>> >> >> >> >> >> - }
>> >> >> >> >> >> - }
>> >> >> >> >> >> + rdma_disconnect(rdma->cm_id);
>> >> >> >> >> >
>> >> >> >> >> > I'm worried whether this change could break stuff:
>> >> >> >> >> > The docs say for rdma_disconnect that it flushes any posted
>> >> >> >> >> > work
>> >> >> >> >> > requests to the completion queue; so unless we wait for the
>> >> >> >> >> > event
>> >> >> >> >> > do we know the stuff has been flushed? In the normal
>> >> >> >> >> > non-cancel case
>> >> >> >> >> > I'm worried that means we could lose something.
>> >> >> >> >> > (But I don't know the rdma/infiniband specs well enough to
>> >> >> >> >> > know if it's
>> >> >> >> >> > really a problem).
>> >> >> >> >>
>> >> >> >> >> In qemu_fclose function, it invoke qemu_fflush(f) before invoke
>> >> >> >> >> f->ops->close.
>> >> >> >> >> so I think it's safe for normal migration case.
>> >> >> >> >>
>> >> >> >> >> For the root cause why not receive RDMA_CM_EVENT_DISCONNECTED
>> >> >> >> >> event
>> >> >> >> >> after rdma_disconnect,
>> >> >> >> >> I loop in Aviad Yehezkel<address@hidden>, Aviad will help us
>> >> >> >> >> find the root cause.
>> >> >> >> >>
>> >> >> >> >> >
>> >> >> >> >> > Dave
>> >> >> >> >> >
>> >> >> >> >> >> trace_qemu_rdma_cleanup_disconnect();
>> >> >> >> >> >> rdma->connected = false;
>> >> >> >> >> >> }
>> >> >> >> >> >> diff --git a/migration/trace-events b/migration/trace-events
>> >> >> >> >> >> index d6be74b..64573ff 100644
>> >> >> >> >> >> --- a/migration/trace-events
>> >> >> >> >> >> +++ b/migration/trace-events
>> >> >> >> >> >> @@ -125,7 +125,6 @@ qemu_rdma_accept_pin_state(bool pin) "%d"
>> >> >> >> >> >> qemu_rdma_accept_pin_verbsc(void *verbs) "Verbs context
>> >> >> >> >> >> after listen: %p"
>> >> >> >> >> >> qemu_rdma_block_for_wrid_miss(const char *wcompstr, int
>> >> >> >> >> >> wcomp, const char *gcompstr, uint64_t req) "A Wanted wrid %s
>> >> >> >> >> >> (%d) but got %s (%" PRIu64 ")"
>> >> >> >> >> >> qemu_rdma_cleanup_disconnect(void) ""
>> >> >> >> >> >> -qemu_rdma_cleanup_waiting_for_disconnect(void) ""
>> >> >> >> >> >> qemu_rdma_close(void) ""
>> >> >> >> >> >> qemu_rdma_connect_pin_all_requested(void) ""
>> >> >> >> >> >> qemu_rdma_connect_pin_all_outcome(bool pin) "%d"
>> >> >> >> >> >> --
>> >> >> >> >> >> 1.8.3.1
>> >> >> >> >> >>
>> >> >> >> >> > --
>> >> >> >> >> > Dr. David Alan Gilbert / address@hidden / Manchester, UK
>> >> >> >> > --
>> >> >> >> > Dr. David Alan Gilbert / address@hidden / Manchester, UK
>> >> >> > --
>> >> >> > Dr. David Alan Gilbert / address@hidden / Manchester, UK
>> >> > --
>> >> > Dr. David Alan Gilbert / address@hidden / Manchester, UK
>> > --
>> > Dr. David Alan Gilbert / address@hidden / Manchester, UK
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
- Re: [Qemu-devel] [PATCH 2/2] migration: not wait RDMA_CM_EVENT_DISCONNECTED event after rdma_disconnect, (continued)
- Re: [Qemu-devel] [PATCH 2/2] migration: not wait RDMA_CM_EVENT_DISCONNECTED event after rdma_disconnect, Dr. David Alan Gilbert, 2018/05/14
- Re: [Qemu-devel] [PATCH 2/2] migration: not wait RDMA_CM_EVENT_DISCONNECTED event after rdma_disconnect, 858585 jemmy, 2018/05/16
- Re: [Qemu-devel] [PATCH 2/2] migration: not wait RDMA_CM_EVENT_DISCONNECTED event after rdma_disconnect, Dr. David Alan Gilbert, 2018/05/16
- Re: [Qemu-devel] [PATCH 2/2] migration: not wait RDMA_CM_EVENT_DISCONNECTED event after rdma_disconnect, 858585 jemmy, 2018/05/16
- Re: [Qemu-devel] [PATCH 2/2] migration: not wait RDMA_CM_EVENT_DISCONNECTED event after rdma_disconnect, Dr. David Alan Gilbert, 2018/05/16
- Re: [Qemu-devel] [PATCH 2/2] migration: not wait RDMA_CM_EVENT_DISCONNECTED event after rdma_disconnect, 858585 jemmy, 2018/05/16
- Re: [Qemu-devel] [PATCH 2/2] migration: not wait RDMA_CM_EVENT_DISCONNECTED event after rdma_disconnect, Dr. David Alan Gilbert, 2018/05/16
- Message not available
- Message not available
- Message not available
- Re: [Qemu-devel] FW: [PATCH 2/2] migration: not wait RDMA_CM_EVENT_DISCONNECTED event after rdma_disconnect, Aviad Yehezkel, 2018/05/17
- Re: [Qemu-devel] FW: [PATCH 2/2] migration: not wait RDMA_CM_EVENT_DISCONNECTED event after rdma_disconnect, 858585 jemmy, 2018/05/17
- Re: [Qemu-devel] FW: [PATCH 2/2] migration: not wait RDMA_CM_EVENT_DISCONNECTED event after rdma_disconnect, Aviad Yehezkel, 2018/05/17
- Re: [Qemu-devel] [PATCH 2/2] migration: not wait RDMA_CM_EVENT_DISCONNECTED event after rdma_disconnect,
858585 jemmy <=
Re: [Qemu-devel] [PATCH 1/2] migration: update index field when delete or qsort RDMALocalBlock, Dr. David Alan Gilbert, 2018/05/08