Re: [PATCH] iov_iter: optimise iter type checking

[Pavel Begunkov <asml.silence@gmail.com>]

On 06/12/2020 16:01, Pavel Begunkov wrote:
> On 21/11/2020 14:37, Pavel Begunkov wrote:
>> The problem here is that iov_iter_is_*() helpers check types for
>> equality, but all iterate_* helpers do bitwise ands. This confuses
>> compilers, so even if some cases were handled separately with
>> iov_iter_is_*(), corresponding ifs in iterate*() right after are not
>> eliminated.
>>
>> E.g. iov_iter_npages() first handles discards, but iterate_all_kinds()
>> still checks for discard iter type and generates unreachable code down
>> the line.
> 
> Ping. This one should be pretty simple

Ping please. Any doubts about this patch?

> 
>>
>>            text    data     bss     dec     hex filename
>> before:   24409     805       0   25214    627e lib/iov_iter.o
>> after:    23977     805       0   24782    60ce lib/iov_iter.o
>>
>> Reviewed-by: Jens Axboe <axboe@kernel.dk>
>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
>> ---
>>  include/linux/uio.h | 10 +++++-----
>>  1 file changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/uio.h b/include/linux/uio.h
>> index 72d88566694e..c5970b2d3307 100644
>> --- a/include/linux/uio.h
>> +++ b/include/linux/uio.h
>> @@ -57,27 +57,27 @@ static inline enum iter_type iov_iter_type(const struct iov_iter *i)
>>  
>>  static inline bool iter_is_iovec(const struct iov_iter *i)
>>  {
>> -	return iov_iter_type(i) == ITER_IOVEC;
>> +	return iov_iter_type(i) & ITER_IOVEC;
>>  }
>>  
>>  static inline bool iov_iter_is_kvec(const struct iov_iter *i)
>>  {
>> -	return iov_iter_type(i) == ITER_KVEC;
>> +	return iov_iter_type(i) & ITER_KVEC;
>>  }
>>  
>>  static inline bool iov_iter_is_bvec(const struct iov_iter *i)
>>  {
>> -	return iov_iter_type(i) == ITER_BVEC;
>> +	return iov_iter_type(i) & ITER_BVEC;
>>  }
>>  
>>  static inline bool iov_iter_is_pipe(const struct iov_iter *i)
>>  {
>> -	return iov_iter_type(i) == ITER_PIPE;
>> +	return iov_iter_type(i) & ITER_PIPE;
>>  }
>>  
>>  static inline bool iov_iter_is_discard(const struct iov_iter *i)
>>  {
>> -	return iov_iter_type(i) == ITER_DISCARD;
>> +	return iov_iter_type(i) & ITER_DISCARD;
>>  }
>>  
>>  static inline unsigned char iov_iter_rw(const struct iov_iter *i)
>>
> 

-- 
Pavel Begunkov