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Message-ID: <20131015150736.GZ26785@twins.programming.kicks-ass.net>
Date: Tue, 15 Oct 2013 17:07:36 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Don Zickus <dzickus@...hat.com>
Cc: dave.hansen@...ux.intel.com, eranian@...gle.com,
ak@...ux.intel.com, jmario@...hat.com,
linux-kernel@...r.kernel.org, acme@...radead.org
Subject: Re: x86, perf: throttling issues with long nmi latencies
On Tue, Oct 15, 2013 at 04:32:27PM +0200, Peter Zijlstra wrote:
>
> This one seems to actually work and is somewhat simpler.
And here's some hackery to avoid that atomic page inc frobbery.
---
lib/usercopy.c | 12 ++++++++--
mm/gup.c | 63 ++++++++++++++++++++++++++++++++++++---------------------
2 files changed, 49 insertions(+), 26 deletions(-)
--- a/arch/x86/lib/usercopy.c
+++ b/arch/x86/lib/usercopy.c
@@ -10,6 +10,8 @@
#include <asm/word-at-a-time.h>
#include <linux/sched.h>
+extern int ___get_user_pages_fast(unsigned long start, int nr_pages, int flags,
+ struct page **pages);
/*
* best effort, GUP based copy_from_user() that is NMI-safe
*/
@@ -18,6 +20,7 @@ copy_from_user_nmi(void *to, const void
{
unsigned long offset, addr = (unsigned long)from;
unsigned long size, len = 0;
+ unsigned long flags;
struct page *page;
void *map;
int ret;
@@ -26,9 +29,12 @@ copy_from_user_nmi(void *to, const void
return len;
do {
- ret = __get_user_pages_fast(addr, 1, 0, &page);
- if (!ret)
+ local_irq_save(flags);
+ ret = ___get_user_pages_fast(addr, 1, 0, &page);
+ if (!ret) {
+ local_irq_restore(flags);
break;
+ }
offset = addr & (PAGE_SIZE - 1);
size = min(PAGE_SIZE - offset, n - len);
@@ -36,7 +42,7 @@ copy_from_user_nmi(void *to, const void
map = kmap_atomic(page);
memcpy(to, map+offset, size);
kunmap_atomic(map);
- put_page(page);
+ local_irq_restore(flags);
len += size;
to += size;
--- a/arch/x86/mm/gup.c
+++ b/arch/x86/mm/gup.c
@@ -63,19 +63,22 @@ static inline pte_t gup_get_pte(pte_t *p
#endif
}
+#define GUPF_GET 0x01
+#define GUPF_WRITE 0x02
+
/*
* The performance critical leaf functions are made noinline otherwise gcc
* inlines everything into a single function which results in too much
* register pressure.
*/
static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
- unsigned long end, int write, struct page **pages, int *nr)
+ unsigned long end, int flags, struct page **pages, int *nr)
{
unsigned long mask;
pte_t *ptep;
mask = _PAGE_PRESENT|_PAGE_USER;
- if (write)
+ if (flags & GUPF_WRITE)
mask |= _PAGE_RW;
ptep = pte_offset_map(&pmd, addr);
@@ -89,7 +92,8 @@ static noinline int gup_pte_range(pmd_t
}
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
page = pte_page(pte);
- get_page(page);
+ if (flags & GUPF_GET)
+ get_page(page);
SetPageReferenced(page);
pages[*nr] = page;
(*nr)++;
@@ -109,7 +113,7 @@ static inline void get_head_page_multipl
}
static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
- unsigned long end, int write, struct page **pages, int *nr)
+ unsigned long end, int flags, struct page **pages, int *nr)
{
unsigned long mask;
pte_t pte = *(pte_t *)&pmd;
@@ -117,7 +121,7 @@ static noinline int gup_huge_pmd(pmd_t p
int refs;
mask = _PAGE_PRESENT|_PAGE_USER;
- if (write)
+ if (flags & GUPF_WRITE)
mask |= _PAGE_RW;
if ((pte_flags(pte) & mask) != mask)
return 0;
@@ -131,19 +135,20 @@ static noinline int gup_huge_pmd(pmd_t p
do {
VM_BUG_ON(compound_head(page) != head);
pages[*nr] = page;
- if (PageTail(page))
+ if ((flags & GUPF_GET) && PageTail(page))
get_huge_page_tail(page);
(*nr)++;
page++;
refs++;
} while (addr += PAGE_SIZE, addr != end);
- get_head_page_multiple(head, refs);
+ if (flags & GUPF_GET)
+ get_head_page_multiple(head, refs);
return 1;
}
static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
- int write, struct page **pages, int *nr)
+ int flags, struct page **pages, int *nr)
{
unsigned long next;
pmd_t *pmdp;
@@ -167,10 +172,10 @@ static int gup_pmd_range(pud_t pud, unsi
if (pmd_none(pmd) || pmd_trans_splitting(pmd))
return 0;
if (unlikely(pmd_large(pmd))) {
- if (!gup_huge_pmd(pmd, addr, next, write, pages, nr))
+ if (!gup_huge_pmd(pmd, addr, next, flags, pages, nr))
return 0;
} else {
- if (!gup_pte_range(pmd, addr, next, write, pages, nr))
+ if (!gup_pte_range(pmd, addr, next, flags, pages, nr))
return 0;
}
} while (pmdp++, addr = next, addr != end);
@@ -179,7 +184,7 @@ static int gup_pmd_range(pud_t pud, unsi
}
static noinline int gup_huge_pud(pud_t pud, unsigned long addr,
- unsigned long end, int write, struct page **pages, int *nr)
+ unsigned long end, int flags, struct page **pages, int *nr)
{
unsigned long mask;
pte_t pte = *(pte_t *)&pud;
@@ -187,7 +192,7 @@ static noinline int gup_huge_pud(pud_t p
int refs;
mask = _PAGE_PRESENT|_PAGE_USER;
- if (write)
+ if (flags & GUPF_WRITE)
mask |= _PAGE_RW;
if ((pte_flags(pte) & mask) != mask)
return 0;
@@ -201,19 +206,20 @@ static noinline int gup_huge_pud(pud_t p
do {
VM_BUG_ON(compound_head(page) != head);
pages[*nr] = page;
- if (PageTail(page))
+ if ((flags & GUPF_GET) && PageTail(page))
get_huge_page_tail(page);
(*nr)++;
page++;
refs++;
} while (addr += PAGE_SIZE, addr != end);
- get_head_page_multiple(head, refs);
+ if (flags & GUPF_GET)
+ get_head_page_multiple(head, refs);
return 1;
}
static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
- int write, struct page **pages, int *nr)
+ int flags, struct page **pages, int *nr)
{
unsigned long next;
pud_t *pudp;
@@ -226,10 +232,10 @@ static int gup_pud_range(pgd_t pgd, unsi
if (pud_none(pud))
return 0;
if (unlikely(pud_large(pud))) {
- if (!gup_huge_pud(pud, addr, next, write, pages, nr))
+ if (!gup_huge_pud(pud, addr, next, flags, pages, nr))
return 0;
} else {
- if (!gup_pmd_range(pud, addr, next, write, pages, nr))
+ if (!gup_pmd_range(pud, addr, next, flags, pages, nr))
return 0;
}
} while (pudp++, addr = next, addr != end);
@@ -241,13 +247,12 @@ static int gup_pud_range(pgd_t pgd, unsi
* Like get_user_pages_fast() except its IRQ-safe in that it won't fall
* back to the regular GUP.
*/
-int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
+int ___get_user_pages_fast(unsigned long start, int nr_pages, int flags,
struct page **pages)
{
struct mm_struct *mm = current->mm;
unsigned long addr, len, end;
unsigned long next;
- unsigned long flags;
pgd_t *pgdp;
int nr = 0;
@@ -255,7 +260,7 @@ int __get_user_pages_fast(unsigned long
addr = start;
len = (unsigned long) nr_pages << PAGE_SHIFT;
end = start + len;
- if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
+ if (unlikely(!access_ok((flags & GUPF_WRITE) ? VERIFY_WRITE : VERIFY_READ,
(void __user *)start, len)))
return 0;
@@ -277,7 +282,6 @@ int __get_user_pages_fast(unsigned long
* (which we do on x86, with the above PAE exception), we can follow the
* address down to the the page and take a ref on it.
*/
- local_irq_save(flags);
pgdp = pgd_offset(mm, addr);
do {
pgd_t pgd = *pgdp;
@@ -285,14 +289,27 @@ int __get_user_pages_fast(unsigned long
next = pgd_addr_end(addr, end);
if (pgd_none(pgd))
break;
- if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
+ if (!gup_pud_range(pgd, addr, next, flags, pages, &nr))
break;
} while (pgdp++, addr = next, addr != end);
- local_irq_restore(flags);
return nr;
}
+int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
+ struct page **pages)
+{
+ unsigned long flags;
+ int ret;
+
+ local_irq_save(flags);
+ ret = ___get_user_pages_fast(start, nr_pages,
+ GUPF_GET | (write ? GUPF_WRITE : 0), pages);
+ local_irq_restore(flags);
+
+ return ret;
+}
+
/**
* get_user_pages_fast() - pin user pages in memory
* @start: starting user address
--
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