Re: [uml-devel] [PATCH 2/2] UML - Speed up exec
From: Blaisorblade
Date: Fri Mar 30 2007 - 18:11:01 EST
On venerdì 30 marzo 2007, Jeff Dike wrote:
> flush_thread doesn't need to do a full page table walk in order to
> clear the address space. It knows what the end result needs to be, so
> it can call unmap directly.
>
> This results in a 10-20% speedup in an exec from bash.
Oh, yeah!
When porting part of Ingo's work, I realized that a similar thing can be done
for fork().
If the whole address space is unmapped in init_new_context_skas(), the first
fix_range_common() call won't need to call unmap at all. He did this with
remap_file_pages(), where init_new_context_skas() must "unmap" everything
anyway.
This is giving some speedup in lmbench (5% better in fork proc, 2% better in
exec proc), but the results are still controversial, there is one benchmark
with a 2% slowdown (called 'mmap latency').
In a loop, it maps, touches a byte per page and unmaps a region with growing
size (up to 32MB).
However, since results aren't yet stable for some other benchmark (context
switching benchmark is crazy), I'm still studying on this.
> Signed-off-by: Jeff Dike <jdike@xxxxxxxxxxxxxxx>
> --
> arch/um/kernel/skas/exec.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> Index: linux-2.6.21-mm/arch/um/kernel/skas/exec.c
> ===================================================================
> --- linux-2.6.21-mm.orig/arch/um/kernel/skas/exec.c 2007-03-30
> 10:28:24.000000000 -0400 +++
> linux-2.6.21-mm/arch/um/kernel/skas/exec.c 2007-03-30 10:30:15.000000000
> -0400 @@ -17,7 +17,17 @@
>
> void flush_thread_skas(void)
> {
> - force_flush_all();
> + void *data = NULL;
> + unsigned long end = proc_mm ? task_size : CONFIG_STUB_START;
> + int ret;
> +
> + ret = unmap(¤t->mm->context.skas.id, 0, end, 1, &data);
> + if(ret){
> + printk("flush_thread_skas - clearing address space failed, "
> + "err = %d\n", ret);
> + force_sig(SIGKILL, current);
> + }
> +
> switch_mm_skas(¤t->mm->context.skas.id);
> }
--
Inform me of my mistakes, so I can add them to my list!
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade
Index: linux-2.6.git/arch/um/include/skas/mmu-skas.h
===================================================================
--- linux-2.6.git.orig/arch/um/include/skas/mmu-skas.h
+++ linux-2.6.git/arch/um/include/skas/mmu-skas.h
@@ -16,6 +16,7 @@ struct mmu_context_skas {
unsigned long last_pmd;
#endif
uml_ldt_t ldt;
+ int first_flush;
};
extern void switch_mm_skas(struct mm_id * mm_idp);
Index: linux-2.6.git/arch/um/kernel/skas/mmu.c
===================================================================
--- linux-2.6.git.orig/arch/um/kernel/skas/mmu.c
+++ linux-2.6.git/arch/um/kernel/skas/mmu.c
@@ -77,6 +77,7 @@ int init_new_context_skas(struct task_st
struct mmu_context_skas *to_mm = &mm->context.skas;
unsigned long stack = 0;
int ret = -ENOMEM;
+ void *unused = NULL;
if(skas_needs_stub){
stack = get_zeroed_page(GFP_KERNEL);
@@ -121,6 +122,14 @@ int init_new_context_skas(struct task_st
else to_mm->id.u.pid = start_userspace(stack);
}
+ mm->context.skas.first_flush = 1;
+ ret = unmap(&mm->context.skas.id, 0, TASK_SIZE, 1, &unused);
+ if (ret < 0) {
+ printk("init_new_context_skas - unmap failed, "
+ "errno = %d; continuing\n", ret);
+ mm->context.skas.first_flush = 0;
+ }
+
ret = init_new_ldt(to_mm, from_mm);
if(ret < 0){
printk("init_new_context_skas - init_ldt"
Index: linux-2.6.git/arch/um/kernel/tlb.c
===================================================================
--- linux-2.6.git.orig/arch/um/kernel/tlb.c
+++ linux-2.6.git/arch/um/kernel/tlb.c
@@ -139,10 +139,17 @@ void fix_range_common(struct mm_struct *
void *flush = NULL;
int op_index = -1, last_op = ARRAY_SIZE(ops) - 1;
int ret = 0;
+ int first_flush;
if(mm == NULL)
return;
+ /* Nothing is mapped in this address space, so no call to add_munmap()
+ * must be done */
+ first_flush = mm->context.skas.first_flush;
+
+ mm->context.skas.first_flush = 0;
+
ops[0].type = NONE;
for(addr = start_addr; addr < end_addr && !ret;){
npgd = pgd_offset(mm, addr);
@@ -151,9 +158,10 @@ void fix_range_common(struct mm_struct *
if(end > end_addr)
end = end_addr;
if(force || pgd_newpage(*npgd)){
- ret = add_munmap(addr, end - addr, ops,
- &op_index, last_op, mmu,
- &flush, do_ops);
+ if (!first_flush)
+ ret = add_munmap(addr, end - addr, ops,
+ &op_index, last_op, mmu,
+ &flush, do_ops);
pgd_mkuptodate(*npgd);
}
addr = end;
@@ -166,9 +174,10 @@ void fix_range_common(struct mm_struct *
if(end > end_addr)
end = end_addr;
if(force || pud_newpage(*npud)){
- ret = add_munmap(addr, end - addr, ops,
- &op_index, last_op, mmu,
- &flush, do_ops);
+ if (!first_flush)
+ ret = add_munmap(addr, end - addr, ops,
+ &op_index, last_op, mmu,
+ &flush, do_ops);
pud_mkuptodate(*npud);
}
addr = end;
@@ -181,9 +190,10 @@ void fix_range_common(struct mm_struct *
if(end > end_addr)
end = end_addr;
if(force || pmd_newpage(*npmd)){
- ret = add_munmap(addr, end - addr, ops,
- &op_index, last_op, mmu,
- &flush, do_ops);
+ if (!first_flush)
+ ret = add_munmap(addr, end - addr, ops,
+ &op_index, last_op, mmu,
+ &flush, do_ops);
pmd_mkuptodate(*npmd);
}
addr = end;
@@ -207,7 +217,8 @@ void fix_range_common(struct mm_struct *
PAGE_SIZE, r, w, x, ops,
&op_index, last_op, mmu,
&flush, do_ops);
- else ret = add_munmap(addr, PAGE_SIZE, ops,
+ else if (!first_flush)
+ ret = add_munmap(addr, PAGE_SIZE, ops,
&op_index, last_op, mmu,
&flush, do_ops);
}
@@ -219,7 +230,7 @@ void fix_range_common(struct mm_struct *
*npte = pte_mkuptodate(*npte);
addr += PAGE_SIZE;
}
- if(!ret)
+ if (!ret && op_index > -1)
ret = (*do_ops)(mmu, ops, op_index, 1, &flush);
/* This is not an else because ret is modified above */