Re: O->A loan

[yamt%mwd.biglobe.ne.jp@localhost (YAMAMOTO Takashi)]

hi,

> yamt%mwd.biglobe.ne.jp@localhost (YAMAMOTO Takashi) wrote:
>> hi,
>> 
>> i'd like to to either fix or remove O->A page loaning.
>> 
>> the biggest problem is the lack of users.  thus no way to test.
>> any ideas?
> 
> After looking at O->A loaning code in yamt-pagecache branch, looking at
> the benchmark results by Jaime (some data was sent privately, I think)
> and contemplating about this mechanism - I tend to think that O->A loaning
> should be removed.  It is a significant code complexity in UVM with some
> special casing and benchmarks indicate that the benefit is somewhat small.
> 
> Does not seem to be worth, does it?

with this particular use alone, i tend to agree.

fwiw, the following is probably one of the best cases for loaned read.

YAMAMOTO Takashi

without loaned read:

        kuma% dd if=/netbsd bs=1m|wc -c
        14+1 records in
        14+1 records out
        14768691 bytes transferred in 0.038 secs (388649763 bytes/sec)
         14768691

with loaned read:

        kuma% dd if=/netbsd bs=1m|wc -c
        14+1 records in
        14+1 records out
        14768691 bytes transferred in 0.023 secs (642117000 bytes/sec)
         14768691

> 
>> 
>> YAMAMOTO Takashi
> 
> -- 
> Mindaugas