[PATCH v2] pseries/hotplug-memory: hot-add: skip redundant LMB lookup
Scott Cheloha
cheloha at linux.ibm.com
Wed Sep 16 03:55:26 AEST 2020
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>
---
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.
arch/powerpc/include/asm/topology.h | 2 +
arch/powerpc/mm/numa.c | 2 +-
.../platforms/pseries/hotplug-memory.c | 101 +++++++-----------
3 files changed, 44 insertions(+), 61 deletions(-)
diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
index f0b6300e7dd3..afd7e0513a65 100644
--- a/arch/powerpc/include/asm/topology.h
+++ b/arch/powerpc/include/asm/topology.h
@@ -96,6 +96,8 @@ static inline int find_and_online_cpu_nid(int cpu)
#endif /* CONFIG_NUMA && CONFIG_PPC_SPLPAR */
+extern int of_drconf_to_nid_single(struct drmem_lmb *);
+
#include <asm-generic/topology.h>
#ifdef CONFIG_SMP
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..f4474ef91fe5 100644
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -388,108 +388,87 @@ static int dlpar_remove_lmb(struct drmem_lmb *lmb)
static int dlpar_memory_remove_by_count(u32 lmbs_to_remove)
{
struct drmem_lmb *lmb;
- int lmbs_removed = 0;
- int lmbs_available = 0;
+ u32 lmbs_available, lmbs_removed;
int rc;
+ boolean readd;
- pr_info("Attempting to hot-remove %d LMB(s)\n", lmbs_to_remove);
+ lmbs_available = lmbs_removed = 0;
+ readd = false;
- if (lmbs_to_remove == 0)
- return -EINVAL;
+ pr_info("attempting to hot-remove %u LMB(s)\n", lmbs_to_remove);
/* Validate that there are enough LMBs to satisfy the request */
for_each_drmem_lmb(lmb) {
- if (lmb_is_removable(lmb))
- lmbs_available++;
-
if (lmbs_available == lmbs_to_remove)
break;
+ if (lmb_is_removable(lmb))
+ lmbs_available++;
}
if (lmbs_available < lmbs_to_remove) {
- pr_info("Not enough LMBs available (%d of %d) to satisfy request\n",
+ pr_info("hot-remove failed: insufficient LMB(s): have %u/%u\n",
lmbs_available, lmbs_to_remove);
return -EINVAL;
}
for_each_drmem_lmb(lmb) {
- rc = dlpar_remove_lmb(lmb);
- if (rc)
+ if (lmbs_removed == lmbs_to_remove)
+ break;
+ if (dlpar_remove_lmb(lmb))
continue;
- /* Mark this lmb so we can add it later if all of the
- * requested LMBs cannot be removed.
+ /*
+ * Success! Mark the LMB so we can readd it later if
+ * the request fails.
*/
drmem_mark_lmb_reserved(lmb);
-
lmbs_removed++;
- if (lmbs_removed == lmbs_to_remove)
- break;
+ pr_debug("hot-removed LMB %u\n", lmb->drc_index);
}
if (lmbs_removed != lmbs_to_remove) {
- pr_err("Memory hot-remove failed, adding LMB's back\n");
-
- for_each_drmem_lmb(lmb) {
- if (!drmem_lmb_reserved(lmb))
- continue;
+ pr_err("hot-remove failed: readding LMB(s)\n");
+ readd = true;
+ }
- rc = dlpar_add_lmb(lmb);
- if (rc)
- pr_err("Failed to add LMB back, drc index %x\n",
+ for_each_drmem_lmb(lmb) {
+ if (!drmem_lmb_reserved(lmb))
+ continue;
+ if (readd) {
+ if (dlpar_add_lmb(lmb)) {
+ pr_err("failed to readd LMB %u\n",
lmb->drc_index);
-
- drmem_remove_lmb_reservation(lmb);
- }
-
- rc = -EINVAL;
- } else {
- for_each_drmem_lmb(lmb) {
- if (!drmem_lmb_reserved(lmb))
- continue;
-
+ }
+ } else
dlpar_release_drc(lmb->drc_index);
- pr_info("Memory at %llx was hot-removed\n",
- lmb->base_addr);
-
- drmem_remove_lmb_reservation(lmb);
- }
- rc = 0;
+ drmem_remove_lmb_reservation(lmb);
}
- return rc;
+ return (readd) ? -EINVAL : 0;
}
static int dlpar_memory_remove_by_index(u32 drc_index)
{
struct drmem_lmb *lmb;
- int lmb_found;
int rc;
- pr_info("Attempting to hot-remove LMB, drc index %x\n", drc_index);
-
lmb_found = 0;
for_each_drmem_lmb(lmb) {
if (lmb->drc_index == drc_index) {
- lmb_found = 1;
rc = dlpar_remove_lmb(lmb);
- if (!rc)
+ if (!rc) {
dlpar_release_drc(lmb->drc_index);
-
- break;
+ pr_info("hot-removed LMB %u\n", drc_index);
+ } else {
+ pr_err("failed to hot-remove LMB %u\n",
+ drc_index);
+ }
+ return rc;
}
}
- if (!lmb_found)
- rc = -EINVAL;
-
- if (rc)
- pr_info("Failed to hot-remove memory at %llx\n",
- lmb->base_addr);
- else
- pr_info("Memory at %llx was hot-removed\n", lmb->base_addr);
-
- return rc;
+ pr_err("failed to hot-remove LMB %u: no such LMB\n", drc_index);
+ return -EINVAL;
}
static int dlpar_memory_remove_by_ic(u32 lmbs_to_remove, u32 drc_index)
@@ -611,8 +590,10 @@ 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);
--
2.24.1
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