[ovs-dev] [PATCH] dpif-netdev: Allocate dp_netdev_pmd_thread struct by xzalloc_cacheline.

Stokes, Ian ian.stokes at intel.com
Fri Dec 8 13:45:44 UTC 2017


> All instances of struct dp_netdev_pmd_thread are allocated by xzalloc and
> therefore doesn't guarantee memory allocation aligned on CACHE_LINE_SIZE
> boundary. Due to this any padding done inside the structure with this
> assumption might create holes.
> 
> This commit replaces xzalloc, free with xzalloc_cacheline and
> free_cacheline. With the changes the memory is 64 byte aligned.

Thanks for this Bhanu,

I think this looks OK and I'm considering pushing to the DPDK_Merge branch but as there has been a fair bit of debate lately regarding memory and cache alignment I want to flag to others who have engaged to date to have their say before I apply it as there has been no input yet for the patch.

@Jan/Ilya, are you ok with this change?

Thanks
Ian

> 
> Before:
>     With xzalloc, all the memory is 16 byte aligned.
> 
>     (gdb) p pmd
>     $1 = (struct dp_netdev_pmd_thread *) 0x7eff8a813010
>     (gdb) p &pmd->cacheline0
>     $2 = (OVS_CACHE_LINE_MARKER *) 0x7eff8a813010
>     (gdb) p &pmd->cacheline1
>     $3 = (OVS_CACHE_LINE_MARKER *) 0x7eff8a813050
>     (gdb) p &pmd->flow_cache
>     $4 = (struct emc_cache *) 0x7eff8a813090
>     (gdb) p &pmd->flow_table
>     $5 = (struct cmap *) 0x7eff8acb30d0
>     (gdb)  p &pmd->stats
>     $6 = (struct dp_netdev_pmd_stats *) 0x7eff8acb3110
>     (gdb) p &pmd->port_mutex
>     $7 = (struct ovs_mutex *) 0x7eff8acb3150
>     (gdb) p &pmd->poll_list
>     $8 = (struct hmap *) 0x7eff8acb3190
>     (gdb) p &pmd->tnl_port_cache
>     $9 = (struct hmap *) 0x7eff8acb31d0
>     (gdb) p &pmd->stats_zero
>     $10 = (unsigned long long (*)[5]) 0x7eff8acb3210
> 
> After:
>     With xzalloc_cacheline, all the memory is 64 byte aligned.
> 
>     (gdb) p pmd
>     $1 = (struct dp_netdev_pmd_thread *) 0x7f39e2365040
>     (gdb) p &pmd->cacheline0
>     $2 = (OVS_CACHE_LINE_MARKER *) 0x7f39e2365040
>     (gdb) p &pmd->cacheline1
>     $3 = (OVS_CACHE_LINE_MARKER *) 0x7f39e2365080
>     (gdb) p &pmd->flow_cache
>     $4 = (struct emc_cache *) 0x7f39e23650c0
>     (gdb) p &pmd->flow_table
>     $5 = (struct cmap *) 0x7f39e2805100
>     (gdb) p &pmd->stats
>     $6 = (struct dp_netdev_pmd_stats *) 0x7f39e2805140
>     (gdb) p &pmd->port_mutex
>     $7 = (struct ovs_mutex *) 0x7f39e2805180
>     (gdb) p &pmd->poll_list
>     $8 = (struct hmap *) 0x7f39e28051c0
>     (gdb) p &pmd->tnl_port_cache
>     $9 = (struct hmap *) 0x7f39e2805200
>     (gdb) p &pmd->stats_zero
>     $10 = (unsigned long long (*)[5]) 0x7f39e2805240
> 
> Reported-by: Ilya Maximets <i.maximets at samsung.com>
> Signed-off-by: Bhanuprakash Bodireddy <bhanuprakash.bodireddy at intel.com>
> ---
>  lib/dpif-netdev.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c index db78318..3e281ae
> 100644
> --- a/lib/dpif-netdev.c
> +++ b/lib/dpif-netdev.c
> @@ -3646,7 +3646,7 @@ reconfigure_pmd_threads(struct dp_netdev *dp)
>      FOR_EACH_CORE_ON_DUMP(core, pmd_cores) {
>          pmd = dp_netdev_get_pmd(dp, core->core_id);
>          if (!pmd) {
> -            pmd = xzalloc(sizeof *pmd);
> +            pmd = xzalloc_cacheline(sizeof *pmd);
>              dp_netdev_configure_pmd(pmd, dp, core->core_id, core-
> >numa_id);
>              pmd->thread = ovs_thread_create("pmd", pmd_thread_main, pmd);
>              VLOG_INFO("PMD thread on numa_id: %d, core id: %2d created.",
> @@ -4574,7 +4574,7 @@ dp_netdev_destroy_pmd(struct dp_netdev_pmd_thread
> *pmd)
>      xpthread_cond_destroy(&pmd->cond);
>      ovs_mutex_destroy(&pmd->cond_mutex);
>      ovs_mutex_destroy(&pmd->port_mutex);
> -    free(pmd);
> +    free_cacheline(pmd);
>  }
> 
>  /* Stops the pmd thread, removes it from the 'dp->poll_threads',
> --
> 2.4.11
> 
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