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RE: [PATCH v2] Limit the amount of work done for each Receiver DPC
- To: "paul@xxxxxxx" <paul@xxxxxxx>, Owen Smith <owen.smith@xxxxxxxxxx>
- From: Martin Harvey <martin.harvey@xxxxxxxxxx>
- Date: Mon, 6 Jun 2022 10:04:07 +0000
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- Thread-topic: [PATCH v2] Limit the amount of work done for each Receiver DPC
-----Original Message-----
From: Durrant, Paul <xadimgnik@xxxxxxxxx>
Sent: 02 June 2022 12:44
To: Owen Smith <owen.smith@xxxxxxxxxx>; Martin Harvey <martin.harvey@xxxxxxxxxx>
Cc: win-pv-devel@xxxxxxxxxxxxxxxxxxxx
Subject: Re: [PATCH v2] Limit the amount of work done for each Receiver DPC
> How does this version look?
Ugggg. Really really no, sorry.
Semantic point 1:
If you look at how it works when both patches are applied, you'll see that
AllFlushed is meant to be kept as a running check as to whether all packets
that could be processed, have been processed at this point. It's not just some
statically determined criteria at the start of the DPC routine as to whether we
will be able to process all the packets in the current DPC.
This is the case when you consider 2/2 when XenNet can abort the processing,
and we re-check the is-list-empty criterion, instead of simply referring to the
"more" variable which had been previously calculated (but is no longer an
accurate indicator of the state of the list).
Bug 2:
- while (!IsListEmpty(&Ring->PacketComplete)) {
+ while (More) {
Well, yes-ish except that More is now not an accurate relection and you have to
recalculate it, and it becomes a bit disingenuous.
TBH it looks a lot better when both patches have been applied, because then
xennet can stop the processing, and at that point it's clear the the
"AllFlushed" flag indicates processing has proceeded as far as it can, and is
not related to some static calculation as to how many packets are left in this
batch.
MH.
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