Module Name: src
Committed By: riastradh
Date: Sat Feb 25 00:32:49 UTC 2023
Modified Files:
src/sys/arch/xen/xen: if_xennet_xenbus.c
Log Message:
xennet(4): Membar audit.
- xennet_tx_complete: Other side owns rsp_prod, giving us responses
to tx commands. We own rsp_cons, recording which responess we've
processed already.
1. Other side initializes responses before advancing rsp_prod, so
we must observe rsp_prod before trying to examine the responses.
Hence load from rsp_prod must be followed by xen_rmb.
(Can this just use atomic_load_acquire?)
2. As soon as other side observes rsp_event, it may start to
overwrite now-unused response slots, so we must finish using the
response before advancing rsp_cons. Hence we must issue xen_wmb
before store to rsp_event.
(Can this just use atomic_store_release?)
(Should this use RING_FINAL_CHECK_FOR_RESPONSES?)
3. When loop is done and we set rsp_event, we must ensure the other
side has had a chance to see that we want more before we check
whether there is more to consume; otherwise the other side might
not bother to send us an interrupt. Hence after setting
rsp_event, we must issue xen_mb (store-before-load) before
re-checking rsp_prod.
- xennet_handler (rx): Same deal, except the xen_mb is buried in
RING_FINAL_CHECK_FOR_RESPONSES. Unclear why xennet_tx_complete has
this open-coded while xennet_handler (rx) uses the macro.
XXX pullup-8 (at least the xen_mb part; requires patch)
XXX pullup-9 (at least the xen_mb part; requires patch)
XXX pullup-10
To generate a diff of this commit:
cvs rdiff -u -r1.128 -r1.129 src/sys/arch/xen/xen/if_xennet_xenbus.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
