Patchwork [v2] powerpc: align DTL buffer to AMS boundary

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Submitter Nishanth Aravamudan
Date April 13, 2011, 10:33 p.m.
Message ID <1302733988-23037-1-git-send-email-nacc@us.ibm.com>
Download mbox | patch
Permalink /patch/91120/
State Superseded
Headers show

Comments

Nishanth Aravamudan - April 13, 2011, 10:33 p.m.
PAPR specifies that DTL buffers can not cross AMS environments (aka CMO
in the PAPR) and can not cross a memory entitlement granule boundary
(4k). This is found in section 14.11.3.2 H_REGISTER_VPA of the PAPR.
kmalloc does not guarantee an alignment of the allocation, though,
beyond 8 bytes (at least in my understanding). Over-allocate and align
the resulting address. Tested both with and without AMS on a p7
partition.

---
Change from v1: removed extraneous #include.

Note, I initially put this in a firmware check if-block, but we have
also seen some issues with alignment with non-AMS partitions. The wasted
memory is unfortunate, though.

Cc: Paul Mackerras <paulus@samba.org>
Cc: Anton Blanchard <anton@samba.org>
Cc: linuxppc-dev@lists.ozlabs.org

 arch/powerpc/platforms/pseries/setup.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)
Michael Ellerman - April 14, 2011, 4:12 a.m.
On Wed, 2011-04-13 at 15:33 -0700, Nishanth Aravamudan wrote:
> PAPR specifies that DTL buffers can not cross AMS environments (aka CMO
> in the PAPR) and can not cross a memory entitlement granule boundary
> (4k). This is found in section 14.11.3.2 H_REGISTER_VPA of the PAPR.
> kmalloc does not guarantee an alignment of the allocation, though,
> beyond 8 bytes (at least in my understanding). Over-allocate and align
> the resulting address.

You can specify alignment by creating your own kmem_cache, ie.
kmem_cache_create().

Obviously there will be some overhead to create the cache structure, but
I'd think it will be less than 4k * NR_CPUs.

cheers

Patch

diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
index 0007241..a67be48 100644
--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -293,14 +293,15 @@  static int alloc_dispatch_logs(void)
 
 	for_each_possible_cpu(cpu) {
 		pp = &paca[cpu];
-		dtl = kmalloc_node(DISPATCH_LOG_BYTES, GFP_KERNEL,
-				   cpu_to_node(cpu));
+		dtl = kmalloc_node(DISPATCH_LOG_BYTES + DISPATCH_LOG_BYTES - 1,
+				   GFP_KERNEL, cpu_to_node(cpu));
 		if (!dtl) {
 			pr_warn("Failed to allocate dispatch trace log for cpu %d\n",
 				cpu);
 			pr_warn("Stolen time statistics will be unreliable\n");
 			break;
 		}
+		dtl = PTR_ALIGN(dtl, DISPATCH_LOG_BYTES);
 
 		pp->dtl_ridx = 0;
 		pp->dispatch_log = dtl;