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Diffstat (limited to 'open_issues/system_call_mechanism.mdwn')
| -rw-r--r-- | open_issues/system_call_mechanism.mdwn | 43 |
1 files changed, 41 insertions, 2 deletions
diff --git a/open_issues/system_call_mechanism.mdwn b/open_issues/system_call_mechanism.mdwn index 5598148c..68418097 100644 --- a/open_issues/system_call_mechanism.mdwn +++ b/open_issues/system_call_mechanism.mdwn @@ -1,4 +1,4 @@ -[[!meta copyright="Copyright © 2011 Free Software Foundation, Inc."]] +[[!meta copyright="Copyright © 2011, 2012 Free Software Foundation, Inc."]] [[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable id="license" text="Permission is granted to copy, distribute and/or modify this @@ -10,8 +10,47 @@ License|/fdl]]."]]"""]] [[!tag open_issue_gnumach]] -IRC, freenode, #hurd, 2011-05-07 +[[!toc]] + + +# IRC, freenode, #hurd, 2011-05-07 <braunr> very simple examples: system calls use old call gates, which are the slowest path to kernel space <braunr> modern processors have dedicated instructions now + + +# IRC, freenode, #hurd, 2012-04-22 + + <braunr> rah: basically, system calls are slower on mach because they use + call gates instead of newer sysenter/sysexit + <youpi> braunr: sysenter/exit is a x86_64 thing + <braunr> rah: apart from that, the code can't get much simpler, and *I* + know, for i have studied it, and wrote a compatible version in a clone + attempt + <youpi> braunr: on a x86_64 port we'd probably use sysenter/exit + <braunr> youpi: no there are 32-bits instructions, i don't remember if + they're called sysenter, it's in my thesis though so i'm sure of it :) + <youpi> braunr: ah, the other part + <youpi> is linux-x86 using them? + <braunr> youpi: yes, glibc uses them + <youpi> and does it really change much nowadays? + <youpi> what is the actual difference between int 80 and sysenter? + <braunr> less checking + <youpi> checking what? + <youpi> the idt? + <braunr> ring levels for example + <youpi> well, checking a ring is fast :) + <braunr> depending on the original and requested levels, there are lookups + in tables + <braunr> sysenter always assume 3 to 0 and 0 to 3 for sysexit + <youpi> ah, also it assumes things about segments + <youpi> so that indeed makes context things simpler + <braunr> right + <braunr> but mach doesn't uses int 0x80 + <braunr> it uses an lcall + <braunr> which is a bit slower from what I could read some time ago + <braunr> (not sure if it's still relevant) + <youpi> actually in 64bit mode I had to catch lcall from the invalid + instruction trap + <youpi> perhaps it got dropped in 64bit mode |