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um: Remove unnecessary faulted check in uaccess.c 

It is not necessary to check if a fault has occured or not
after disabling pagefaults. kmap_atomic does that in all
cases and we can disable it for 64 bit where kmap is not needed
and a simple page_address would suffice.

dd if=/dev/zero of=/dev/null bs=1M count=1M
Before: 3.1GB/s. After: 3.5GB/s

There is a noticeable difference for file disk read and write
as well as less noticeable difference for network IO.

Signed-off-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
This commit is contained in:
Anton Ivanov 2018-11-22 14:45:13 +00:00 committed by Richard Weinberger
parent 50109b5a03
commit 747b254ca2
1 changed files with 12 additions and 11 deletions
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23
arch/um/kernel/skas/uaccess.c
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@ -62,27 +62,28 @@ static int do_op_one_page(unsigned long addr, int len, int is_write,
jmp_buf buf;
struct page *page;
pte_t *pte;
int n, faulted;
int n;
pte = maybe_map(addr, is_write);
if (pte == NULL)
return -1;
page = pte_page(*pte);
#ifdef CONFIG_64BIT
pagefault_disable();
addr = (unsigned long) page_address(page) +
(addr & ~PAGE_MASK);
#else
addr = (unsigned long) kmap_atomic(page) +
(addr & ~PAGE_MASK);
#endif
n = (*op)(addr, len, arg);
current->thread.fault_catcher = &buf;
faulted = UML_SETJMP(&buf);
if (faulted == 0)
n = (*op)(addr, len, arg);
else
n = -1;
current->thread.fault_catcher = NULL;
#ifdef CONFIG_64BIT
pagefault_enable();
#else
kunmap_atomic((void *)addr);
#endif
return n;
}