by Anton Blanchard

[permalink] [raw]

Subject: Re: [PATCH v2 1/2] powerpc/drmem: accelerate memory_add_physaddr_to_nid() with LMB xarray

Hi Scott,

I'm hitting this issue and Rick just pointed my at your patch. Any
chance we could get it upstream?

Thanks,
Anton

> On PowerPC, memory_add_physaddr_to_nid() uses a linear search to find
> an LMB matching the given address. This scales very poorly when there
> are many LMBs. The poor scaling cripples drmem_init() during boot:
> lmb_set_nid(), which calls memory_add_physaddr_to_nid(), is called for
> each LMB.
>
> If we index each LMB in an xarray by its base address we can achieve
> O(log n) search during memory_add_physaddr_to_nid(), which scales much
> better.
>
> For example, in the lab we have a 64TB P9 machine with 256MB LMBs.
> So, suring drmem_init() we instantiate 249854 LMBs. On a vanilla
> kernel it completes drmem_init() in ~35 seconds with a soft lockup
> trace. On the patched kernel it completes drmem_init() in ~0.5
> seconds.
>
> Before:
> [ 53.721639] drmem: initializing drmem v2
> [ 80.604346] watchdog: BUG: soft lockup - CPU#65 stuck for 23s!
> [swapper/0:1] [ 80.604377] Modules linked in:
> [ 80.604389] CPU: 65 PID: 1 Comm: swapper/0 Not tainted 5.6.0-rc2+
> #4 [ 80.604397] NIP: c0000000000a4980 LR: c0000000000a4940 CTR:
> 0000000000000000 [ 80.604407] REGS: c0002dbff8493830 TRAP: 0901
> Not tainted (5.6.0-rc2+) [ 80.604412] MSR: 8000000002009033
> <SF,VEC,EE,ME,IR,DR,RI,LE> CR: 44000248 XER: 0000000d [
> 80.604431] CFAR: c0000000000a4a38 IRQMASK: 0 [ 80.604431] GPR00:
> c0000000000a4940 c0002dbff8493ac0 c000000001904400 c0003cfffffede30 [
> 80.604431] GPR04: 0000000000000000 c000000000f4095a
> 000000000000002f 0000000010000000 [ 80.604431] GPR08:
> c0000bf7ecdb7fb8 c0000bf7ecc2d3c8 0000000000000008 c00c0002fdfb2001 [
> 80.604431] GPR12: 0000000000000000 c00000001e8ec200 [ 80.604477]
> NIP [c0000000000a4980] hot_add_scn_to_nid+0xa0/0x3e0 [ 80.604486]
> LR [c0000000000a4940] hot_add_scn_to_nid+0x60/0x3e0 [ 80.604492]
> Call Trace: [ 80.604498] [c0002dbff8493ac0] [c0000000000a4940]
> hot_add_scn_to_nid+0x60/0x3e0 (unreliable) [ 80.604509]
> [c0002dbff8493b20] [c000000000087c10]
> memory_add_physaddr_to_nid+0x20/0x60 [ 80.604521]
> [c0002dbff8493b40] [c0000000010d4880] drmem_init+0x25c/0x2f0 [
> 80.604530] [c0002dbff8493c10] [c000000000010154]
> do_one_initcall+0x64/0x2c0 [ 80.604540] [c0002dbff8493ce0]
> [c0000000010c4aa0] kernel_init_freeable+0x2d8/0x3a0 [ 80.604550]
> [c0002dbff8493db0] [c000000000010824] kernel_init+0x2c/0x148 [
> 80.604560] [c0002dbff8493e20] [c00000000000b648]
> ret_from_kernel_thread+0x5c/0x74 [ 80.604567] Instruction dump: [
> 80.604574] 392918e8 e9490000 e90a000a e92a0000 80ea000c 1d080018
> 3908ffe8 7d094214 [ 80.604586] 7fa94040 419d00dc e9490010 714a0088
> <2faa0008> 409e00ac e9490000 7fbe5040 [ 89.047390] drmem: 249854
> LMB(s)
>
> After:
> [ 53.424702] drmem: initializing drmem v2
> [ 53.898813] drmem: 249854 LMB(s)
>
> lmb_set_nid() is called from dlpar_lmb_add() so this patch will also
> improve memory hot-add speeds on big machines.
>
> Signed-off-by: Scott Cheloha <[email protected]>
> ---
> arch/powerpc/include/asm/drmem.h | 1 +
> arch/powerpc/mm/drmem.c | 24 ++++++++++++++++++++++++
> arch/powerpc/mm/numa.c | 29 ++++++++++-------------------
> 3 files changed, 35 insertions(+), 19 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/drmem.h
> b/arch/powerpc/include/asm/drmem.h index 3d76e1c388c2..90a5a9ad872b
> 100644 --- a/arch/powerpc/include/asm/drmem.h
> +++ b/arch/powerpc/include/asm/drmem.h
> @@ -88,6 +88,7 @@ static inline bool drmem_lmb_reserved(struct
> drmem_lmb *lmb) return lmb->flags & DRMEM_LMB_RESERVED;
> }
>
> +struct drmem_lmb *drmem_find_lmb_by_base_addr(u64 base_addr);
> u64 drmem_lmb_memory_max(void);
> void __init walk_drmem_lmbs(struct device_node *dn,
> void (*func)(struct drmem_lmb *, const
> __be32 **)); diff --git a/arch/powerpc/mm/drmem.c
> b/arch/powerpc/mm/drmem.c index 44bfbdae920c..62cbe79e3860 100644
> --- a/arch/powerpc/mm/drmem.c
> +++ b/arch/powerpc/mm/drmem.c
> @@ -11,12 +11,31 @@
> #include <linux/of.h>
> #include <linux/of_fdt.h>
> #include <linux/memblock.h>
> +#include <linux/xarray.h>
> #include <asm/prom.h>
> #include <asm/drmem.h>
>
> +static DEFINE_XARRAY(drmem_lmb_xa_base_addr);
> static struct drmem_lmb_info __drmem_info;
> struct drmem_lmb_info *drmem_info = &__drmem_info;
>
> +static int drmem_cache_lmb_for_lookup(struct drmem_lmb *lmb)
> +{
> + void *ret;
> +
> + ret = xa_store(&drmem_lmb_xa_base_addr, lmb->base_addr, lmb,
> + GFP_KERNEL);
> + if (xa_is_err(ret))
> + return xa_err(ret);
> +
> + return 0;
> +}
> +
> +struct drmem_lmb *drmem_find_lmb_by_base_addr(u64 base_addr)
> +{
> + return xa_load(&drmem_lmb_xa_base_addr, base_addr);
> +}
> +
> u64 drmem_lmb_memory_max(void)
> {
> struct drmem_lmb *last_lmb;
> @@ -364,6 +383,8 @@ static void __init init_drmem_v1_lmbs(const
> __be32 *prop)
> for_each_drmem_lmb(lmb) {
> read_drconf_v1_cell(lmb, &prop);
> + if (drmem_cache_lmb_for_lookup(lmb) != 0)
> + return;
> lmb_set_nid(lmb);
> }
> }
> @@ -411,6 +432,9 @@ static void __init init_drmem_v2_lmbs(const
> __be32 *prop) lmb->aa_index = dr_cell.aa_index;
> lmb->flags = dr_cell.flags;
>
> + if (drmem_cache_lmb_for_lookup(lmb) != 0)
> + return;
> +
> lmb_set_nid(lmb);
> }
> }
> diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> index 3c7dec70cda0..0fd7963a991e 100644
> --- a/arch/powerpc/mm/numa.c
> +++ b/arch/powerpc/mm/numa.c
> @@ -958,27 +958,18 @@ early_param("topology_updates",
> early_topology_updates); static int
> hot_add_drconf_scn_to_nid(unsigned long scn_addr) {
> struct drmem_lmb *lmb;
> - unsigned long lmb_size;
> - int nid = NUMA_NO_NODE;
> -
> - lmb_size = drmem_lmb_size();
> -
> - for_each_drmem_lmb(lmb) {
> - /* skip this block if it is reserved or not assigned
> to
> - * this partition */
> - if ((lmb->flags & DRCONF_MEM_RESERVED)
> - || !(lmb->flags & DRCONF_MEM_ASSIGNED))
> - continue;
> -
> - if ((scn_addr < lmb->base_addr)
> - || (scn_addr >= (lmb->base_addr + lmb_size)))
> - continue;
>
> - nid = of_drconf_to_nid_single(lmb);
> - break;
> - }
> + lmb = drmem_find_lmb_by_base_addr(scn_addr);
> + if (lmb == NULL)
> + return NUMA_NO_NODE;
> +
> + /* can't use this block if it is reserved or not assigned to
> + * this partition */
> + if ((lmb->flags & DRCONF_MEM_RESERVED)
> + || !(lmb->flags & DRCONF_MEM_ASSIGNED))
> + return NUMA_NO_NODE;
>
> - return nid;
> + return of_drconf_to_nid_single(lmb);
> }
>
> /*