gwj / at91sam9263 · Commits

  • Use writeback caching by default with qcow2 ...
    4dc822d7 
    qcow2 writes a cluster reference count on every cluster update.  This causes
performance to crater when using anything but cache=writeback.  This is most
noticeable when using savevm.  Right now, qcow2 isn't a reliable format
regardless of the type of cache your using because metadata is not updated in
the correct order.  Considering this, I think it's somewhat reasonable to use
writeback caching by default with qcow2 files.

It at least avoids the massive performance regression for users until we sort
out the issues in qcow2. 

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



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  • Add ballooning infrastructure. ...
    df751fa8 
    Balloon devices allow you to ask the guest to allocate memory.  This allows you
to release that memory.  It's mostly useful for freeing up large chunks of
memory from cooperative guests.

Ballooning is supported by both Xen and VirtIO.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



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  • Add virtio-blk support ...
    6e02c38d 
    Virtio-blk is a paravirtual block device based on VirtIO.  It can be used by
specifying the if=virtio parameter to the -drive parameter.

When using -enable-kvm, it can achieve very good performance compared to IDE or
SCSI.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



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  • Revert r5636 to fix icount on hosts w/o high-res clocks ...
    357c692c 
    Changeset r5636 changed the timers to run in the alarm callback.  The 
alarm callback can only be called as frequently as the host alarm timer 
fires.  For older Linux hosts and possibly non-Linux hosts, this can be 
as high as a 1ms granularity.

icount calculates the select timeout based on the next deadline and 
select is usually capable of sleeping for a short period of time than 
alarm timer granularity.  This means that changing the timer callbacks 
to be based on alarm firing caused timers to fire much later than they 
ought to when using icount.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



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  • gdbstub: manage CPUs as threads (Jan Kiszka) ...
    880a7578 
    This patch enhances QEMU's built-in debugger for SMP guest debugging.
Using the thread support of the gdb remote protocol, each VCPU is mapped
on a pseudo thread and exposed to the gdb frontend. This way you can
easy switch the focus of gdb between the VCPUs and observe their states.
On breakpoint hit, the focus is automatically adjusted just as for
normal multi-threaded application under gdb control.

Furthermore, the patch propagates breakpoint and watchpoint insertions
or removals to all CPUs, not just the current one as it was the case so
far. Without this, SMP guest debugging was practically unfeasible.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



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  • Remove dumb_refresh ...
    2ad1a437 
    It is safe not to set dpy_refresh and that's used to indicate that the display
doesn't need updates.  This saves us two wakeups per second.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



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  • Move network redirection code out of vl.c and into net.c ...
    63a01ef8 
    Mostly code motion.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



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  • Move CharDriverState code out of vl.c ...
    6f97dba0 
    The motivating goal behind this is to allow other tools to use the CharDriver
code.  This patch is pure code motion except for the Makefile changes and the
copyright/header in qemu-char.c.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



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  • Move some declarations around in the QEMU CharDriver code ...
    0e82f34d 
    The goal of this series is to move the CharDriverState code out of vl.c and
into its own file, qemu-char.c.  This patch moves around some declarations so
the next patch can be pure code motion.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



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  • Increase default IO timeout from 10ms to 5s ...
    0a1af395 
    With the recent changes to the main loop, we no longer have unconditional
polling.  This means we can now sleep in select() for much longer than we
previously did.  This patch increases our select() sleep time from 10ms to 5s
which is effectively unlimited since we're going to wake up sooner than that
in almost all circumstances.

With this patch, I see the number of wake-ups with an idle dynamic ticks guest
drop from 80 per second to about 15 times per second.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



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  • Main loop fixes/cleanup ...
    56f3a5d0 
    Tidy up win32 main loop bits, allow timeout >= 1s, and force timeout to 0 if
there is a pending bottom half.



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  • Implement "info chardev" command. (Gerd Hoffmann) ...
    5ccfae10 
    This patch makes qemu keep track of the character devices in use and
implements a "info chardev" monitor command to print a list.

qemu_chr_open() sticks the devices into a linked list now.  It got a new
argument (label), so there is a name for each device.  It also assigns a
filename to each character device.  By default it just copyes the
filename passed in.  Individual drivers can fill in something else
though.  qemu_chr_open_pty() sets the filename to name of the pseudo tty
allocated.

Output looks like this:

  (qemu) info chardev
  monitor: filename=unix:/tmp/run.sh-26827/monitor,server,nowait
  serial0: filename=unix:/tmp/run.sh-26827/console,server
  serial1: filename=pty:/dev/pts/5
  parallel0: filename=vc:640x480

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



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  • Make DMA bottom-half driven (v2) ...
    492c30af 
    The current DMA routines are driven by a call in main_loop_wait() after every
select.

This patch converts the DMA code to be driven by a constantly rescheduled
bottom half.  The advantage of using a scheduled bottom half is that we can
stop scheduling the bottom half when there no DMA channels are runnable.  This
means we can potentially detect this case and sleep longer in the main loop.

The only two architectures implementing DMA_run() are cris and i386.  For cris,
I converted it to a simple repeating bottom half.  I've only compile tested
this as cris does not seem to work on a 64-bit host.  It should be functionally
identical to the previous implementation so I expect it to work.

For x86, I've made sure to only fire the DMA bottom half if there is a DMA
channel that is runnable.  The effect of this is that unless you're using sb16
or a floppy disk, the DMA bottom half never fires.

You probably should test this malc.  My own benchmarks actually show slight
improvement by it's possible the change in timing could affect your demos.

Since v1, I've changed the code to use a BH instead of a timer.  cris at least
seems to depend on faster than 10ms polling.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



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  • Make bottom halves more robust ...
    1b435b10 
    Bottom halves are supposed to not complete until the next iteration of the main
loop.  This is very important to ensure that guests can not cause stack
overflows in the block driver code.  Right now, if you attempt to schedule a
bottom half within a bottom half callback, you will enter an infinite loop.

This patch uses the same logic that we use for the IOHandler loop to make the
bottom half processing robust in list manipulation while in a callback.

This patch also introduces idle scheduling for bottom halves.  qemu_bh_poll()
returns an indication of whether any bottom halves were successfully executed.
qemu_aio_wait() uses this to immediately return if a bottom half was executed
instead of waiting for a completion notification.

qemu_bh_schedule_idle() works around this by not reporting the callback has
run in the qemu_bh_poll loop.  qemu_aio_wait() probably needs some refactoring
but that would require a larger code audit.  idle scheduling seems like a good
compromise.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>




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  • Expand cache= option and use write-through caching by default ...
    9f7965c7 
    This patch changes the cache= option to accept none, writeback, or writethough
to control the host page cache behavior.  By default, writethrough caching is
now used which internally is implemented by using O_DSYNC to open the disk
images.  When using -snapshot, writeback is used by default since data integrity
it not at all an issue.

cache=none has the same behavior as cache=off previously.  The later syntax is
still supported by now deprecated.  I also cleaned up the O_DIRECT
implementation to avoid many of the #ifdefs.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



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  • Fix IO performance regression in sparc ...
    9e472e10 
    Replace signalfd with signal handler/pipe.  There is no way to interrupt
the CPU execution loop when a file descriptor becomes readable.  This
results in a large performance regression in sparc emulation during
bootup.
   
This patch switches us to signal handler/pipe which was originally
suggested by Ian Jackson.  The signal handler lets us interrupt the
CPU emulation loop while the write to a pipe lets us avoid the
select/signal race condition.
    
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



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