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Submit #1699

Updated by tuxillo almost 9 years ago

Hi, 

 

 It has been suggested that one of the steps towards a proper tickless kernel  
  
 would be the conversion of all the users of the various timeout API  
  
 to the use of the more rounded time units whenever possible, e.g. the  
  
 less precise and more rounded seconds instead of the more precise ticks. [0]   
   
 In the kernel, the most obvious and popular examples of such API  
  
 would be callout(9) and tsleep(9). 
 
 Since many current users of these API logically require an ms-based timer,  
  
 and the future granularity of a tick may be subject to change, it also  
  
 makes sense to introduce a millisecond (_ms) version of the API together with  
  
 the second (_s) addition. 

 

 It may be noted that OpenBSD already has had similar functions introduced  
  
 sometime in 2008 ([1], [2]): timeout_add_{tv,ts,bt,sec,msec,usec,nsec}.   
   
 Apart from _sec and _msec, the rest have no users (only _usec is used once),  
  
 and in the current environment, the us and ns timeouts would appear to serve  
  
 no purpose other than to mislead and confuse the developer.   
   
 On the other hand, timeout_add_sec is referenced in 142 kernel source files  
  
 in OpenBSD 4.7 as of 2010-03, and timeout_add_msec -- in 79.   
   
 Also, the standard SI abbreviation for second and millisecond  
  
 is s and ms, respectively, not sec and msec. 

 

 I think it may actually be reasonable to introduce a decisecond (ds)  
  
 version of the functions (in addition to the second and millisecond),  
  
 since that's what many millisecond-to-be users actually need, and _ds  
  
 would be more tickless-friendly compared to _ms anyways.   
   
 The centisecond (cs) may be considered as a more distant option.    :-) 

 

 Please let me know what you think of these additions, and whether  
  
 similar _s and _ms sleep(9) functions should be added as well.   
   
 I'm also interested in the feedback regarding the potential _ds  
  
 addition. 

 

 Best regards, 
 
 Constantine. 

 

 [0] http://oss.intel.com/pdfs/maximum_tickless.pdf "Getting maximum mileage out of tickless" (2007) 
 
 [1] http://www.openbsd.org/cgi-bin/cvsweb/src/sys/kern/kern_timeout.c#rev1.27 "timeout_add_{tv,ts,bt,sec,usec,nsec}" (2008-07-11) 
 
 [2] http://www.openbsd.org/cgi-bin/cvsweb/src/sys/kern/kern_timeout.c#rev1.29 "timeout_add_msec" (2008-10-22)

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