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spml/ucx: shuffle EPs creation #12907

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@michal-shalev
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What?

This PR randomize the order in which endpoints (EPs) are created in the mca_spml_ucx_add_procs function. Each new EP is placed at a random position instead of cyclic order.

Why?

Recently, a customer raised concerns about incast behavior during SHMEM quiet operations, where many EPs communicating in a fixed order could lead to network congestion and performance degradation. They believe that randomizing the order of EPs could reduce the likelihood of incast collisions.
The customer is interested in testing a patch to address this.

How?

Used the Fisher-Yates shuffle algorithm to randomize indices and modified the loop to handle all indices, including 0, within a single pass.

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github-actions bot commented Nov 4, 2024

Hello! The Git Commit Checker CI bot found a few problems with this PR:

b734683: spml/ucx: shuffle EPs creation

  • check_signed_off: does not contain a valid Signed-off-by line

Please fix these problems and, if necessary, force-push new commits back up to the PR branch. Thanks!

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github-actions bot commented Nov 4, 2024

Hello! The Git Commit Checker CI bot found a few problems with this PR:

4d562ac: spml/ucx: shuffle EPs creation

  • check_signed_off: does not contain a valid Signed-off-by line

Please fix these problems and, if necessary, force-push new commits back up to the PR branch. Thanks!

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github-actions bot commented Nov 4, 2024

Hello! The Git Commit Checker CI bot found a few problems with this PR:

2345c1f: spml/ucx: shuffle EPs creation

  • check_signed_off: does not contain a valid Signed-off-by line

Please fix these problems and, if necessary, force-push new commits back up to the PR branch. Thanks!

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github-actions bot commented Nov 4, 2024

Hello! The Git Commit Checker CI bot found a few problems with this PR:

489dbcf: spml/ucx: shuffle EPs creation

  • check_signed_off: does not contain a valid Signed-off-by line

Please fix these problems and, if necessary, force-push new commits back up to the PR branch. Thanks!

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github-actions bot commented Nov 4, 2024

Hello! The Git Commit Checker CI bot found a few problems with this PR:

eb303bf: spml/ucx: shuffle EPs creation

  • check_signed_off: does not contain a valid Signed-off-by line

Please fix these problems and, if necessary, force-push new commits back up to the PR branch. Thanks!

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github-actions bot commented Nov 4, 2024

Hello! The Git Commit Checker CI bot found a few problems with this PR:

25c6b86: spml/ucx: shuffle EPs creation

  • check_signed_off: does not contain a valid Signed-off-by line

Please fix these problems and, if necessary, force-push new commits back up to the PR branch. Thanks!

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github-actions bot commented Nov 4, 2024

Hello! The Git Commit Checker CI bot found a few problems with this PR:

893a73e: spml/ucx: shuffle EPs creation

  • check_signed_off: does not contain a valid Signed-off-by line

Please fix these problems and, if necessary, force-push new commits back up to the PR branch. Thanks!

@michal-shalev
spml/ucx: shuffle EPs creation
03c59cd 
Signed-off-by: Michal Shalev <mshalev.nvidia.com>
gleon99
gleon99 reviewed Nov 4, 2024
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tvegas1
tvegas1 reviewed Nov 4, 2024
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minor comments

oshmem/mca/spml/ucx/spml_ucx.c Outdated
}
}

indices = malloc(nprocs * sizeof(int));
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minor: sizeof(*indices)

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done

oshmem/mca/spml/ucx/spml_ucx.c Outdated
/* Get the EP connection requests for all the processes from modex */
for (n = 0; n < nprocs; ++n) {
i = (my_rank + n) % nprocs;
for (i = nprocs - 1; i >= 0; --i) {
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maybe perform randomization as a separate function/loop

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The idea here is to iterate over the EPs once, and to save another iteration

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ok for me, but i guess one extra loop on sequential memory on ep creation would not impact perf

oshmem/mca/spml/ucx/spml_ucx.c Outdated
&mca_spml_ucx_ctx_default.ucp_peers[i].ucp_conn);
&mca_spml_ucx_ctx_default.ucp_peers[indices[i]].ucp_conn);
if (UCS_OK != err) {
SPML_UCX_ERROR("ucp_ep_create(proc=%zu/%zu) failed: %s", n, nprocs,
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also update log line index (i and indices[i])

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Notice I'm using proc_index instead of i.
I changed n to proc_index, why indices[proc_index]? the loop still iterates until nproc.

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ah right, already up-to-date. we could add indices[proc_index] to the log along with iteration since it is randomized.

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done

@michal-shalev
spml/ucx: fix for loop
78d0a63 
Signed-off-by: Michal Shalev <mshalev.nvidia.com>
@michal-shalev
spml/ucx: PR fixes
32a86a4 
Signed-off-by: Michal Shalev <mshalev.nvidia.com>
gleon99
gleon99 reviewed Nov 7, 2024
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oshmem/mca/spml/ucx/spml_ucx.c
ucp_address_t **wk_local_addr;
unsigned int *wk_addr_len;
ucp_ep_params_t ep_params;
int *indices;
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unsigned int?

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Please notice proc_index >= 0;

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Exactly..

@michal-shalev
spml/ucx: fix swap
6dc87d1 
Signed-off-by: Michal Shalev <mshalev.nvidia.com>
@michal-shalev
spml/ucx: PR fixes 2.0
2ad0f14 
Signed-off-by: Michal Shalev <mshalev.nvidia.com>
@gleon99
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gleon99 commented Mar 2, 2025

The customer is not responsive (e-mail discussion),

@gleon99 gleon99 closed this Mar 2, 2025
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