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Re: [Qemu-devel] [PATCH v3 23/29] bitmap: add atomic set functions
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v3 23/29] bitmap: add atomic set functions |
Date: |
Wed, 27 May 2015 11:41:05 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 |
On 27/05/2015 09:58, Fam Zheng wrote:
> On Tue, 05/26 18:54, Paolo Bonzini wrote:
>> From: Stefan Hajnoczi <address@hidden>
>>
>> Use atomic_or() for atomic bitmaps where several threads may set bits at
>> the same time. This avoids the race condition between threads loading
>> an element, bitwise ORing, and then storing the element.
>>
>> When setting all bits in a word we can avoid atomic ops and instead just
>> use an smp_mb() at the end.
>>
>> Most bitmap users don't need atomicity so introduce new functions.
>>
>> Signed-off-by: Stefan Hajnoczi <address@hidden>
>> Message-Id: <address@hidden>
>> [Avoid barrier in the single word case, use full barrier instead of write.
>> - Paolo]
>> Signed-off-by: Paolo Bonzini <address@hidden>
>> ---
>> include/qemu/bitmap.h | 2 ++
>> include/qemu/bitops.h | 14 ++++++++++++++
>> util/bitmap.c | 38 ++++++++++++++++++++++++++++++++++++++
>> 3 files changed, 54 insertions(+)
>>
>> diff --git a/include/qemu/bitmap.h b/include/qemu/bitmap.h
>> index f0273c9..3e0a4f3 100644
>> --- a/include/qemu/bitmap.h
>> +++ b/include/qemu/bitmap.h
>> @@ -39,6 +39,7 @@
>> * bitmap_empty(src, nbits) Are all bits zero in *src?
>> * bitmap_full(src, nbits) Are all bits set in *src?
>> * bitmap_set(dst, pos, nbits) Set specified bit area
>> + * bitmap_set_atomic(dst, pos, nbits) Set specified bit area with atomic
>> ops
>
> The tab/space mix is not consistent. Fixing can be on top.
>
>> * bitmap_clear(dst, pos, nbits) Clear specified bit area
>> * bitmap_find_next_zero_area(buf, len, pos, n, mask) Find bit free
>> area
>> */
>> @@ -226,6 +227,7 @@ static inline int bitmap_intersects(const unsigned long
>> *src1,
>> }
>>
>> void bitmap_set(unsigned long *map, long i, long len);
>> +void bitmap_set_atomic(unsigned long *map, long i, long len);
>> void bitmap_clear(unsigned long *map, long start, long nr);
>> unsigned long bitmap_find_next_zero_area(unsigned long *map,
>> unsigned long size,
>> diff --git a/include/qemu/bitops.h b/include/qemu/bitops.h
>> index 8abdcf9..8164225 100644
>> --- a/include/qemu/bitops.h
>> +++ b/include/qemu/bitops.h
>> @@ -16,6 +16,7 @@
>> #include <assert.h>
>>
>> #include "host-utils.h"
>> +#include "atomic.h"
>>
>> #define BITS_PER_BYTE CHAR_BIT
>> #define BITS_PER_LONG (sizeof (unsigned long) * BITS_PER_BYTE)
>> @@ -39,6 +40,19 @@ static inline void set_bit(long nr, unsigned long *addr)
>> }
>>
>> /**
>> + * set_bit_atomic - Set a bit in memory atomically
>> + * @nr: the bit to set
>> + * @addr: the address to start counting from
>> + */
>> +static inline void set_bit_atomic(long nr, unsigned long *addr)
>> +{
>> + unsigned long mask = BIT_MASK(nr);
>> + unsigned long *p = addr + BIT_WORD(nr);
>> +
>> + atomic_or(p, mask);
>> +}
>
> Where is this function used?
In cpu_physical_memory_set_dirty_flag (patch 25).
Paolo
- [Qemu-devel] [PATCH v3 10/29] kvm: accept non-mapped memory in kvm_dirty_pages_log_change, (continued)
- [Qemu-devel] [PATCH v3 10/29] kvm: accept non-mapped memory in kvm_dirty_pages_log_change, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 13/29] ram_addr: tweaks to xen_modified_memory, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 09/29] memory: track DIRTY_MEMORY_CODE in mr->dirty_log_mask, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 22/29] memory: do not touch code dirty bitmap unless TCG is enabled, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 05/29] memory: differentiate memory_region_is_logging and memory_region_get_dirty_log_mask, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 04/29] display: add memory_region_sync_dirty_bitmap calls, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 15/29] exec: move functions to translate-all.h, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 23/29] bitmap: add atomic set functions, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 19/29] exec: pass client mask to cpu_physical_memory_set_dirty_range, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 07/29] framebuffer: check memory_region_is_logging, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 11/29] memory: include DIRTY_MEMORY_MIGRATION in the dirty log mask, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 16/29] translate-all: remove unnecessary argument to tb_invalidate_phys_range, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 21/29] exec: only check relevant bitmaps for cleanliness, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 24/29] bitmap: add atomic test and clear, Paolo Bonzini, 2015/05/26
- [Qemu-devel] [PATCH v3 14/29] exec: use memory_region_get_dirty_log_mask to optimize dirty tracking, Paolo Bonzini, 2015/05/26