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

open_issues/xen_lseek: ... here.

4 files changed, 25 insertions, 20 deletions

diff --git a/open_issues/performance/io_system/binutils_ld_64ksec.mdwn b/open_issues/performance/io_system/binutils_ld_64ksec.mdwn
index d0b8ea7f..931fd0ee 100644
--- a/open_issues/performance/io_system/binutils_ld_64ksec.mdwn
+++ b/open_issues/performance/io_system/binutils_ld_64ksec.mdwn
@@ -27,10 +27,6 @@ extracted from cdf7c161ebd4a934c9e705d33f5247fd52975612 sources, 2010-10-24.
 On the idle grubber, this one repeatedly takes a few minutes wall time to
 complete successfully, contrary to a few seconds on a GNU/Linux system.
 
-> On order of slowness may in fact be due to a Xen-specific issue, see
-> [[xen_lseek]].  (But there are probably still one or two orders left, even
-> without Xen.)
-
 While processing the object files, there is heavy interaction with the relevant
 [[hurd/translator/ext2fs]] process.  Running [[hurd/debugging/rpctrace]] on
 the testee shows that (primarily) an ever-repeating series of `io_seek` and
@@ -38,19 +34,6 @@ the testee shows that (primarily) an ever-repeating series of `io_seek` and
 shows the equivalent thing (`_llseek`, `read`) -- but Linux' I/O system isn't
 as slow as the Hurd's.
 
----
-
-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
-
-Also see testcase [[test-lseek.c]] and [[test-mach.c]]
-
-[[!tag open_issue_xen]]
+As Samuel figured out later, this slowness may in fact be due to a Xen-specific
+issue, see [[Xen_lseek]].  After the latter has been addressed, we can
+re-evaluate this issue here.
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 :)
diff --git a/open_issues/performance/io_system/test-lseek.c b/open_issues/xen_lseek/test-lseek.c
index 667dce66..667dce66 100644
--- a/open_issues/performance/io_system/test-lseek.c
+++ b/open_issues/xen_lseek/test-lseek.c
diff --git a/open_issues/performance/io_system/test-mach.c b/open_issues/xen_lseek/test-mach.c
index 90337346..90337346 100644
--- a/open_issues/performance/io_system/test-mach.c
+++ b/open_issues/xen_lseek/test-mach.c