On 5/17/2018 5:42 AM, 858585 jemmy wrote:
On Wed, May 16, 2018 at 11:11 PM, Aviad Yehezkel
<avia...@dev.mellanox.co.il> wrote:
Hi Lidong and David,
Sorry for the late response, I had to ramp up on migration code and build a
setup on my side.
PSB my comments for this patch below.
For the RDMA post-copy patches I will comment next week after testing on
Mellanox side too.
Thanks!
On 5/16/2018 5:21 PM, Aviad Yehezkel wrote:
-----Original Message-----
From: Dr. David Alan Gilbert [mailto:dgilb...@redhat.com]
Sent: Wednesday, May 16, 2018 4:13 PM
To: 858585 jemmy <jemmy858...@gmail.com>
Cc: Aviad Yehezkel <avia...@mellanox.com>; Juan Quintela
<quint...@redhat.com>; qemu-devel <qemu-devel@nongnu.org>; Gal Shachaf
<gal...@mellanox.com>; Adi Dotan <ad...@mellanox.com>; Lidong Chen
<lidongc...@tencent.com>
Subject: Re: [PATCH 2/2] migration: not wait RDMA_CM_EVENT_DISCONNECTED
event after rdma_disconnect
* 858585 jemmy (jemmy858...@gmail.com) 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.
I will ask internally and get back on this one.
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.
It is good that the qemu fix solved this issue but me and my colleagues
think we need 2/2 patch anyway.
According to IB Spec once active side send DREQ message he should wait for
DREP message and only once it arrived it should trigger a DISCONNECT event.
DREP message can be dropped due to network issues.
For that case the spec defines a DREP_timeout state in the CM state machine,
if the DREP is dropped we should get a timeout and a TIMEWAIT_EXIT event
will be trigger.
Unfortunately the current kernel CM implementation doesn't include the
DREP_timeout state and in above scenario we will not get DISCONNECT or
TIMEWAIT_EXIT events.
(Similar scenario exists also for passive side).
We think it is best to apply this patch until we will enhance the kernel
code.
Hi Aviad:
How long about the DREP_timeout state?
Do RDMA have some tools like tcpdump? then I can use to confirm whether
DREP message has received.
Thanks.
Are you running IB or RoCE?
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.
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 <lidongc...@tencent.com>
---
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<avia...@mellanox.com>, Aviad will help
us
find the root cause.
Regarding previous discussion on that thread:
rdma_disconnect can be invoke even without invoking ib_dreg_mr first.
common teardown flow:
rdma_disconnect
<-- here resources like QPs are still alive and can DMA to RAM
rdma_destroy_cm_id
<-- All resources are destroyed by MR can be still active
rdma_dreg_mr
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 / dgilb...@redhat.com / Manchester, UK
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
