hotspot-gc-dev Digest, Vol 24, Issue 6

Tony Printezis Antonios.Printezis at
Tue Jun 9 15:15:18 UTC 2009


Dan Hicks wrote:
> Well, my experience is quite different, but I suppose it may have to 
> do with what you consider "overhead".  I've seen GC consume half the 
> CPU cycles (and more), but if you have enough CPU then I guess that's 
> OK.  A big unknown is the cost of the read and write barriers, in 
> terms of both cycles spent and loss of optimization.
Well, our GCs (minus G1) only have a simple card table write barrier and 
no read barrier. The card table barrier doesn't cost you much most of 
the time (maybe a few single digit percent) and it allows much more 
efficient generational GC, which is a win overall.

>> Message: 1
>> Date: Mon, 08 Jun 2009 13:05:54 -0400
>> From: Tony Printezis <Antonios.Printezis at>
>> Subject: Re: GC benchmarks
>> To: Paul Hohensee <Paul.Hohensee at>
>> Cc: hotspot-gc-dev at, Dan Hicks <danhicks at>
>> Message-ID: <4A2D44F2.1010209 at>
>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>> Hi all,
>> The reality these days is that, with a bit of effort in tuning the 
>> GC, GC overhead in applications is really very low (single digit 
>> percentage, sometimes even as low as 1% or 2%). The actual overhead / 
>> pause times / etc. are very application dependent. So, if you come up 
>> with a say synthetic benchmark that does mostly GC, I don't know 
>> whether you'll learn anything by comparing how our GCs perform on it. 
>> We have a few such benchmarks, but they are mainly used for stress 
>> testing, not performance testing.
>> Tony
> ---
> Dan Hicks
> The eyes of others our prisons; their thoughts our cages.  --Virginia 
> Woolf

| Tony Printezis, Staff Engineer   | Sun Microsystems Inc.          |
|                                  | MS UBUR02-311                  |
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