open_issues/performance/io_system/binutils_ld_64ksec: Move Xen lseek stuff...

open_issues/xen_lseek: ... here.

1 files changed, 22 insertions, 0 deletions

diff --git a/open_issues/xen_lseek.mdwn b/open_issues/xen_lseek.mdwn
index accc7c8f..756abf5e 100644
--- a/open_issues/xen_lseek.mdwn
+++ b/open_issues/xen_lseek.mdwn
@@ -10,6 +10,17 @@ License|/fdl]]."]]"""]]
 
 [[!tag open_issue_xen]]
 
+IRC, freenode, #hurd, 2011-09-01:
+
+    <youpi> hum, f951 does myriads of   71->io_seek_request (32768 0) = 0 32768
+    <youpi> no wonder it's slow
+    <youpi> unfortunately that's also what it does on linux, the system call is
+      just less costly
+    <youpi> apparently gfortran calls io_seek for, like, every token of the
+      sourced file
+    <youpi> (fgetpos actually, but that's the same)
+    <youpi> and it is indeed about 10 times slower under Xen for some reason
+
 IRC, freenode, #hurd, 2011-11-02:
 
     <youpi> btw, we have a performance issue with xen
@@ -33,3 +44,14 @@ IRC, freenode, #hurd, 2011-11-02:
       http://www.gnu.org/software/hurd/open_issues/performance/io_system/binutils_ld_64ksec.html
 
 [[performance/io_system/binutils_ld_64ksec]].
+
+Also see the simple testcases [[test-lseek.c]] and [[test-mach.c]].
+
+IRC, freenode, #hurd, 2011-11-05:
+
+    <youpi> [test-mach.c is] mostly as a reference for the trap overhead
+    <youpi> 0.56µs (xen) vs 0.48µs(kvm) on test-mach
+    <youpi> 455µs(xen) vs 16µs(kvm) on test-lseek
+    <youpi> that might simply be an issue in the RPC  mechanism, which behaves
+      badly with the xen memory management
+    <youpi> yes, about 0.5ms for an lseek, that's quite high :)