On Thu, Apr 23, 2020 at 6:29 AM Eelco Chaudron <[email protected]> wrote:
>
> Hi Ben et al.
>
> We recently had an issue where OVS would crash as it was running out of
> stack space processing an OVN flow loop :) I was hoping it would jump
> out of the loop, but due to change, "790c5d269 ofproto-dpif: Do not
> count resubmit to later tables against limit." the resubmit loop can be
> up to 4K.
>
> When the clone action is used (and others) the stack size increases
> quite drastically, some tests showed that over 19M was needed to reach
> the 4K limit. Even a simple resubmit to resubmit jump back and forth
> till 4K is reached requires a 3.5M stack size.
>
> Some small changes, like doing malloc for mf_subvalue, and actset_stub
> in clone_xlate_actions() allowed the worst case to go from around 19M to
> 12M, but still, this is a lot of stack memory.
>
> One idea could be that on the last action in the list try to unwind the
> stack (recursion) to the previous nonfinal action and then continue
> processing this action. I'm not too familiar with the xlate code, but it
> looks quite complex already, so not sure if this is an option :) Also
> not sure if this gives us enough relief in all the OVN scenario as they
> use a lot of resubmits in a single action list.
>
> Another idea Dumitru had was to delay clone() execution until you get
> back to the root actionset. So when you hit a clone() action you store
> the state in the ctx, and then go over the list once you return (this
> could result in a growing list). But you do not end up processing the
> clones on the branch of the tree. The only problem is that this results
> in out of order processing of the action list, i.e. clone(resubmit(,5)),
> 2. Will first sent out the packet on 2 and then on the destination on
> the clone() action. I guess this is a blocking thing, as the OpenFlow
> specification specifies action lists should be executed in order.
>
> Any other ideas on the above or on how to optimize the stack usage?
>
Hi Eelco,
Can we just increase the stack space to a larger value?
Ex: setting ulimit -s to 32Mb
William
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