Re: Predictable CPU discovery

[Rin Okuyama <rokuyama.rk%gmail.com@localhost>]

Hi,

First of all, thank you Jared for finding it out. We didn't notice
that.

On 2020/07/03 23:53, Jason Thorpe wrote:
> > On Jul 3, 2020, at 7:48 AM, Jared McNeill <jmcneill%invisible.ca@localhost> wrote:
> >
> > Considering that we define MAXCPUS=256 for Arm64 and will likely need to bump that limit in the near future, what kind of impact will this have on boot times of large systems?
>
> Dunno -- I suppose it'll have to be measured.

Alternatively, other ports use uvm_page_recolor(9) when secondary
CPUs are attached:

https://nxr.netbsd.org/source/s?refs=uvm_page_recolor&project=src

For aarch64, something like the attached patch makes sense? (Sorry,
compile-test only since I don't have big.LITTLE processors...)

Thanks,
rin

Index: sys/arch/aarch64/aarch64/cpufunc.c
===================================================================
RCS file: /home/netbsd/src/sys/arch/aarch64/aarch64/cpufunc.c,v
retrieving revision 1.21
diff -p -u -r1.21 cpufunc.c
--- sys/arch/aarch64/aarch64/cpufunc.c	1 Jul 2020 07:59:16 -0000	1.21
+++ sys/arch/aarch64/aarch64/cpufunc.c	3 Jul 2020 15:06:15 -0000
@@ -37,6 +37,8 @@ __KERNEL_RCSID(0, "$NetBSD: cpufunc.c,v 
 #include <sys/kmem.h>
 #include <sys/cpu.h>
 
+#include <uvm/uvm_page.h>
+
 #include <aarch64/cpufunc.h>
 
 u_int cputype;			/* compat arm */
@@ -102,6 +104,7 @@ aarch64_getcacheinfo(int unit)
 {
 	struct cpu_info * const ci = curcpu();
 	uint32_t clidr, ctr;
+	u_int vindexsize;
 	int level, cachetype;
 	struct aarch64_cache_info *cinfo = NULL;
 
@@ -215,14 +218,19 @@ aarch64_getcacheinfo(int unit)
 	    ((cinfo[0].cacheable == CACHE_CACHEABLE_ICACHE) ||
 	     (cinfo[0].cacheable == CACHE_CACHEABLE_IDCACHE))) {
 
-		aarch64_cache_vindexsize =
+		vindexsize =
 		    cinfo[0].icache.cache_size /
 		    cinfo[0].icache.cache_ways;
 
-		KASSERT(aarch64_cache_vindexsize != 0);
-		aarch64_cache_prefer_mask = aarch64_cache_vindexsize - 1;
+		KASSERT(vindexsize != 0);
 	} else {
-		aarch64_cache_vindexsize = 0;
+		vindexsize = 0;
+	}
+
+	if (vindexsize > aarch64_cache_vindexsize) {
+		aarch64_cache_vindexsize = vindexsize;
+		aarch64_cache_prefer_mask = vindexsize - 1;
+		uvm_page_recolor(vindexsize / PAGE_SIZE);
 	}
 }