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Differential D5164

HyperV/vmm: improve locking of hv_ring_buffer
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Authored by howard0su_gmail.com on Feb 2 2016, 5:10 AM.
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honzhan_microsoft.com
decui_microsoft.com
sepherosa_gmail.com
royger
adrian
Summary
  1. convert spin lock to def lock
  2. reading always happen in single thread, remove lock protection

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rS FreeBSD src repository - subversion
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Buildable 2358
Build 2374: arc lint + arc unit

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howard0su_gmail.com updated this revision to Diff 12940.Feb 2 2016, 5:10 AM
howard0su_gmail.com retitled this revision from to HyperV/vmm: improve locking of hv_ring_buffer.
howard0su_gmail.com updated this object.
howard0su_gmail.com edited the test plan for this revision. (Show Details)
Herald added subscribers: Contributor Reviews (src), imp. · View Herald TranscriptFeb 2 2016, 5:10 AM
howard0su_gmail.com added reviewers: decui_microsoft.com, honzhan_microsoft.com, adrian, royger.Feb 5 2016, 12:08 PM
howard0su_gmail.com added a reviewer: sepherosa_gmail.com.
sepherosa_gmail.com accepted this revision.Feb 5 2016, 12:17 PM
sepherosa_gmail.com edited edge metadata.

Seems reasonable to me

This revision is now accepted and ready to land.Feb 5 2016, 12:17 PM
adrian added inline comments.Feb 6 2016, 6:21 PM
sys/dev/hyperv/vmbus/hv_ring_buffer.c
357

So this is nit picking, but do yo need memory barriers here if you intend to peek? the lock ends up being effectively a memory barrier..

howard0su_gmail.com added a comment.Feb 22 2016, 2:32 AM

No. Since read/peek are happened in single thread, no mb is needed. Peek is just a normal read except it copies less data and doesn't advance the read position.

sepherosa_gmail.com added a comment.Feb 24 2016, 5:26 AM

I just double checked the code. It is not MPSAFE to process the recv ring w/o lock, e.g. storvsc_poll(), which could be called in another thread. I think the spinlock -> default mtx change should be fine.

sepherosa_gmail.com added a comment.Feb 24 2016, 5:29 AM
In D5164#115390, @sepherosa_gmail.com wrote:

I just double checked the code. It is not MPSAFE to process the recv ring w/o lock, e.g. storvsc_poll(), which could be called in another thread. I think the spinlock -> default mtx change should be fine.

I think we could pass a flag down to the recv ring read/peek, so that we could do lockless read for other drivers.

howard0su_gmail.com abandoned this revision.Apr 21 2016, 2:45 AM

Revision Contents
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sys/
dev/
hyperv/
vmbus/
18 lines

Diff 12940

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sys/dev/hyperv/vmbus/hv_ring_buffer.c

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