[PATCH v4] pseries/hotplug-memory: hot-add: skip redundant LMB lookup
Laurent Dufour
ldufour at linux.ibm.com
Fri Sep 18 00:34:33 AEST 2020
Le 16/09/2020 à 16:51, Scott Cheloha a écrit :
> During memory hot-add, dlpar_add_lmb() calls memory_add_physaddr_to_nid()
> to determine which node id (nid) to use when later calling __add_memory().
>
> This is wasteful. On pseries, memory_add_physaddr_to_nid() finds an
> appropriate nid for a given address by looking up the LMB containing the
> address and then passing that LMB to of_drconf_to_nid_single() to get the
> nid. In dlpar_add_lmb() we get this address from the LMB itself.
>
> In short, we have a pointer to an LMB and then we are searching for
> that LMB *again* in order to find its nid.
>
> If we call of_drconf_to_nid_single() directly from dlpar_add_lmb() we
> can skip the redundant lookup. The only error handling we need to
> duplicate from memory_add_physaddr_to_nid() is the fallback to the
> default nid when drconf_to_nid_single() returns -1 (NUMA_NO_NODE) or
> an invalid nid.
>
> Skipping the extra lookup makes hot-add operations faster, especially
> on machines with many LMBs.
>
> Consider an LPAR with 126976 LMBs. In one test, hot-adding 126000
> LMBs on an upatched kernel took ~3.5 hours while a patched kernel
> completed the same operation in ~2 hours:
>
> Unpatched (12450 seconds):
> Sep 9 04:06:31 ltc-brazos1 drmgr[810169]: drmgr: -c mem -a -q 126000
> Sep 9 04:06:31 ltc-brazos1 kernel: pseries-hotplug-mem: Attempting to hot-add 126000 LMB(s)
> [...]
> Sep 9 07:34:01 ltc-brazos1 kernel: pseries-hotplug-mem: Memory at 20000000 (drc index 80000002) was hot-added
>
> Patched (7065 seconds):
> Sep 8 21:49:57 ltc-brazos1 drmgr[877703]: drmgr: -c mem -a -q 126000
> Sep 8 21:49:57 ltc-brazos1 kernel: pseries-hotplug-mem: Attempting to hot-add 126000 LMB(s)
> [...]
> Sep 8 23:27:42 ltc-brazos1 kernel: pseries-hotplug-mem: Memory at 20000000 (drc index 80000002) was hot-added
>
> It should be noted that the speedup grows more substantial when
> hot-adding LMBs at the end of the drconf range. This is because we
> are skipping a linear LMB search.
>
> To see the distinction, consider smaller hot-add test on the same
> LPAR. A perf-stat run with 10 iterations showed that hot-adding 4096
> LMBs completed less than 1 second faster on a patched kernel:
>
> Unpatched:
> Performance counter stats for 'drmgr -c mem -a -q 4096' (10 runs):
>
> 104,753.42 msec task-clock # 0.992 CPUs utilized ( +- 0.55% )
> 4,708 context-switches # 0.045 K/sec ( +- 0.69% )
> 2,444 cpu-migrations # 0.023 K/sec ( +- 1.25% )
> 394 page-faults # 0.004 K/sec ( +- 0.22% )
> 445,902,503,057 cycles # 4.257 GHz ( +- 0.55% ) (66.67%)
> 8,558,376,740 stalled-cycles-frontend # 1.92% frontend cycles idle ( +- 0.88% ) (49.99%)
> 300,346,181,651 stalled-cycles-backend # 67.36% backend cycles idle ( +- 0.76% ) (50.01%)
> 258,091,488,691 instructions # 0.58 insn per cycle
> # 1.16 stalled cycles per insn ( +- 0.22% ) (66.67%)
> 70,568,169,256 branches # 673.660 M/sec ( +- 0.17% ) (50.01%)
> 3,100,725,426 branch-misses # 4.39% of all branches ( +- 0.20% ) (49.99%)
>
> 105.583 +- 0.589 seconds time elapsed ( +- 0.56% )
>
> Patched:
> Performance counter stats for 'drmgr -c mem -a -q 4096' (10 runs):
>
> 104,055.69 msec task-clock # 0.993 CPUs utilized ( +- 0.32% )
> 4,606 context-switches # 0.044 K/sec ( +- 0.20% )
> 2,463 cpu-migrations # 0.024 K/sec ( +- 0.93% )
> 394 page-faults # 0.004 K/sec ( +- 0.25% )
> 442,951,129,921 cycles # 4.257 GHz ( +- 0.32% ) (66.66%)
> 8,710,413,329 stalled-cycles-frontend # 1.97% frontend cycles idle ( +- 0.47% ) (50.06%)
> 299,656,905,836 stalled-cycles-backend # 67.65% backend cycles idle ( +- 0.39% ) (50.02%)
> 252,731,168,193 instructions # 0.57 insn per cycle
> # 1.19 stalled cycles per insn ( +- 0.20% ) (66.66%)
> 68,902,851,121 branches # 662.173 M/sec ( +- 0.13% ) (49.94%)
> 3,100,242,882 branch-misses # 4.50% of all branches ( +- 0.15% ) (49.98%)
>
> 104.829 +- 0.325 seconds time elapsed ( +- 0.31% )
>
> This is consistent. An add-by-count hot-add operation adds LMBs
> greedily, so LMBs near the start of the drconf range are considered
> first. On an otherwise idle LPAR with so many LMBs we would expect to
> find the LMBs we need near the start of the drconf range, hence the
> smaller speedup.
>
> Signed-off-by: Scott Cheloha <cheloha at linux.ibm.com>
Reviewed-by: Laurent Dufour <ldufour at linux.ibm.com>
> ---
> Changelog:
>
> v1: https://lore.kernel.org/linuxppc-dev/20200910175637.2865160-1-cheloha@linux.ibm.com/
>
> v2:
> - Move prototype for of_drconf_to_nid_single() to topology.h.
> Requested by Michael Ellerman.
>
> v3:
> - Send the right patch. v2 is from the wrong branch, my mistake.
>
> v4:
> - Fix checkpatch.pl warnings. Reported by Laurent Dufour.
>
> arch/powerpc/include/asm/topology.h | 3 +++
> arch/powerpc/mm/numa.c | 2 +-
> arch/powerpc/platforms/pseries/hotplug-memory.c | 6 ++++--
> 3 files changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
> index f0b6300e7dd3..ae19b19f9d44 100644
> --- a/arch/powerpc/include/asm/topology.h
> +++ b/arch/powerpc/include/asm/topology.h
> @@ -86,6 +86,9 @@ static inline int cpu_distance(__be32 *cpu1_assoc, __be32 *cpu2_assoc)
>
> #endif /* CONFIG_NUMA */
>
> +struct drmem_lmb;
> +int of_drconf_to_nid_single(struct drmem_lmb *lmb);
> +
> #if defined(CONFIG_NUMA) && defined(CONFIG_PPC_SPLPAR)
> extern int find_and_online_cpu_nid(int cpu);
> #else
> diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> index 1f61fa2148b5..63507b47164d 100644
> --- a/arch/powerpc/mm/numa.c
> +++ b/arch/powerpc/mm/numa.c
> @@ -430,7 +430,7 @@ static int of_get_assoc_arrays(struct assoc_arrays *aa)
> * This is like of_node_to_nid_single() for memory represented in the
> * ibm,dynamic-reconfiguration-memory node.
> */
> -static int of_drconf_to_nid_single(struct drmem_lmb *lmb)
> +int of_drconf_to_nid_single(struct drmem_lmb *lmb)
> {
> struct assoc_arrays aa = { .arrays = NULL };
> int default_nid = NUMA_NO_NODE;
> diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
> index 0ea976d1cac4..9a533acf8ad0 100644
> --- a/arch/powerpc/platforms/pseries/hotplug-memory.c
> +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
> @@ -611,8 +611,10 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb)
>
> block_sz = memory_block_size_bytes();
>
> - /* Find the node id for this address. */
> - nid = memory_add_physaddr_to_nid(lmb->base_addr);
> + /* Find the node id for this LMB. Fake one if necessary. */
> + nid = of_drconf_to_nid_single(lmb);
> + if (nid < 0 || !node_possible(nid))
> + nid = first_online_node;
>
> /* Add the memory */
> rc = __add_memory(nid, lmb->base_addr, block_sz);
>
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