Messages in this thread | | | Date | Mon, 31 Jan 2022 16:26:06 -0500 (EST) | From | Mathieu Desnoyers <> | Subject | Re: [RFC PATCH 1/2] rseq: extend struct rseq with numa node id |
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----- On Jan 31, 2022, at 4:19 PM, Florian Weimer fw@deneb.enyo.de wrote:
> * Mathieu Desnoyers: > >> Adding the NUMA node id to struct rseq is a straightforward thing to do, >> and a good way to figure out if anything in the user-space ecosystem >> prevents extending struct rseq. >> >> This NUMA node id field allows memory allocators such as tcmalloc to >> take advantage of fast access to the current NUMA node id to perform >> NUMA-aware memory allocation. >> >> It is also useful for implementing NUMA-aware user-space mutexes. > > It can be used to implement getcpu purely in userspace, too. I had > plan to hack this together with a node ID cache in TLS, which should > offer pretty much the same functionality (except for weird CPU > topology changes which alter the node ID of a previously used CPU).
I suspect that any approach based on a user-space cache will break with respect to CRIU. That is one big advantage of using the rseq thread area for this.
> > However, I do not understand the need for two fields here. Why isn't > one enough?
As stated in my self-reply, I don't think those two fields are needed after all.
> > One field would also avoid the need to mess with rseq_cpu_id_state, > maintaining API compatibility.
True. However considering that we plan to remove the buggy "rseq_cs.ptr" fields from the API, that rseq.h UAPI compatibility does not seem to be very much relevant.
But still, it's better if we can avoid breaking API, agreed. And the "node_id_start" does not appear to be needed after all.
Thanks,
Mathieu
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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