Re: [Xen-devel] [libvirt] [PATCH 00/10] libxl: switch driver to use a single libxl_ctx

[Michal Privoznik <mprivozn@xxxxxxxxxx>]

On 18.02.2015 04:56, Jim Fehlig wrote:
> This series is a follow up to
> 
> https://www.redhat.com/archives/libvir-list/2015-February/msg00024.html
> 
> It goes a step further and changes the libxl driver to use one,
> driver-wide libxl_ctx.  Currently the libxl driver has one driver-wide
> ctx for operations that are not domain-specific and a ctx for each
> domain.  This approach was necessary back in the old Xen4.1 libxl days,
> but with the newer libxl it is more of a hinderance than benefit.
> Ian Jackson suggested moving to a single ctx while discussing some
> deadlocks and assertions encountered in the libxl driver when under
> load from tests such as OpenStack Tempest.
> 
> Making such a change involves quite a bit of code movement.  I've tried
> to split that up into a reviewable series,  the result of which are the
> 9 patches that follow.  I've ran this through all of my automated tests
> as well as some hacky tests I created to reproduce failures revealed by
> Tempest.
> 
> One downside of moving to a single ctx is losing the per-domain log
> files.  Currently, a single log stream can be associated with ctx, hence
> all logging from libxl will go to a single file.  Ian is going to
> investigate possibilities to accommodate per-domain log files in libxl,
> but in the meantime folks using Xen are accustomed to a single
> log file from the xend days.
> 
> I've been testing this series on xen-unstable and Xen 4.4.1 + commits
> 2ffeb5d7, 4b9143e4, 5a968257, 60ce518a, 66bff9fd, 77a1bf37, f49f9b41,
> 6b5a5bba, 93699882d, f1335f0d, and 8bc64413.  Results are much better
> than before applying the series, but I do notice a stuck hypercall
> after many (hundreds) concurrent domain create/destroy operations.
> The single libxl_ctx is locked in the callpath, essentially deadlocking
> the driver.
> 
> Thread 1 (Thread 0x7f0649a198c0 (LWP 2235)):
>  0  0x00007f0645272397 in ioctl () from /lib64/libc.so.6
>  1  0x00007f0645d8e353 in linux_privcmd_hypercall (xch=<optimized out>,
>     h=<optimized out>, hypercall=<optimized out>) at xc_linux_osdep.c:134
>  2  0x00007f0645d854b8 in do_xen_hypercall (xch=xch@entry=0x7f0630039390, 
>     hypercall=hypercall@entry=0x7fffd53f80e0) at xc_private.c:249
>  3  0x00007f0645d86aa4 in do_sysctl (sysctl=sysctl@entry=0x7fffd53f8080, 
>     xch=xch@entry=0x7f0630039390) at xc_private.h:281
>  4  xc_sysctl (xch=xch@entry=0x7f0630039390,
>     sysctl=sysctl@entry=0x7fffd53f8170) at xc_private.c:656
>  5  0x00007f0645d7bfbf in xc_domain_getinfolist (xch=0x7f0630039390, 
>     first_domain=first_domain@entry=119, max_domains=max_domains@entry=1, 
>     info=info@entry=0x7fffd53f8260) at xc_domain.c:382
>  6  0x00007f0645fabca6 in domain_death_xswatch_callback
>     (egc=0x7fffd53f83f0, w=<optimized out>, wpath=<optimized out>,
>     epath=<optimized out>) at libxl.c:1041
>  7  0x00007f0645fd75a8 in watchfd_callback (egc=0x7fffd53f83f0,
>     ev=<optimized out>, fd=<optimized out>, events=<optimized out>,
>     revents=<optimized out>) at libxl_event.c:515
>  8  0x00007f0645fd8ac3 in libxl_osevent_occurred_fd (ctx=<optimized out>, 
>     for_libxl=<optimized out>, fd=<optimized out>,
>     events_ign=<optimized out>, revents_ign=<optimized out>) at
>     libxl_event.c:1259
>  9  0x00007f063a23402c in libxlFDEventCallback (watch=454, fd=33,
>     vir_events=1, fd_info=0x7f0608007e70) at libxl/libxl_driver.c:123
> 
> There is no hint in any logs or dmesg suggesting a cause for the stuck
> hypercall.  Any suggestions for further debugging tips appreciated.
> 
> Jim Fehlig (10):
>   libxl: remove redundant calls to libxl_evdisable_domain_death
>   libxl: use libxl_ctx passed to libxlConsoleCallback
>   libxl: use driver-wide ctx in fd and timer event handling
>   libxl: Move setup of child processing code to driver initialization
>   libxl: move event registration to driver initialization
>   libxl: use global libxl_ctx in event handler
>   libxl: remove unnecessary libxlDomainEventsRegister
>   libxl: make libxlDomainFreeMem static
>   libxl: remove per-domain libxl_ctx
>   libxl: change libxl log stream to ERROR log level
> 
>  src/libxl/libxl_conf.c      |   2 +-
>  src/libxl/libxl_domain.c    | 438 ++++++---------------------------------
>  src/libxl/libxl_domain.h    |  27 +--
>  src/libxl/libxl_driver.c    | 484 
> +++++++++++++++++++++++++++++++-------------
>  src/libxl/libxl_migration.c |  17 +-
>  5 files changed, 426 insertions(+), 542 deletions(-)
> 

ACK series

Michal

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel