lkml.org 
[lkml]   [1997]   [Dec]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: copy-bit macro
On 11 Dec 1997, Stefan Monnier wrote:

> "Theodore Y. Ts'o" <tytso@MIT.EDU> writes:
> > (1 << OUT_FLAG_NUMBER) : 0") both involve an assembly language
> > conditional jump instruction, which is expensive, because it involves
> > pipeline stalls, etc.
>
> Has it been measured ? I know that branch prediction is not 100%, but
> I'm just trying to make sure we're not trying to solve a non-problem (if the
> prediction works well, then the jump costs 0 (zero) cycles).

If you have (working) branch prediction the direct cost will be
negligible, if any. But the indirect cost is that you use a slot
in the branch table which means you might well take the full cost
somewhere else later...

Mike

--
.----------------------------------------------------------------------.
| Mike Jagdis | Internet: mailto:mike@roan.co.uk |
| Roan Technology Ltd. | |
| 54A Peach Street, Wokingham | Telephone: +44 118 989 0403 |
| RG40 1XG, ENGLAND | Fax: +44 118 989 1195 |
`----------------------------------------------------------------------'


\
 
 \ /
  Last update: 2005-03-22 13:40    [W:0.053 / U:0.500 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site