Re: x86, perf: throttling issues with long nmi latencies

From: Don Zickus
Date: Tue Oct 15 2013 - 12:23:14 EST

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On Tue, Oct 15, 2013 at 05:07:36PM +0200, Peter Zijlstra wrote:
> 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.

Hmm, for some reason, I did not see much noticable improvement (over your
second patch) with this patch. :-( Not to say it doesn't improve things,
I just don't have hard numbers to see if it is a small percentage better
or not.

Cheers,
Don

>
> ---
> 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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Next message: Joe Perches: "Re: [PATCH 02/18] net: use wrapper functions of net_ratelimit() tosimplify code"
Previous message: Joe Perches: "Re: [PATCH] x86: Run checksumming in parallel accross multiple alu's"
In reply to: Don Zickus: "Re: x86, perf: throttling issues with long nmi latencies"
Next in thread: Don Zickus: "Re: x86, perf: throttling issues with long nmi latencies"
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