Day One
This is my first effort at blogging so bear with me. I'll be posting my thoughts on virtualization, networking, security, and FreeBSD.
View ArticleFreeBSD and sun4v
For a while I worked on sun4v support for FreeBSD. I'm quite fond of the architecture and enjoyed working with the person who was my primary contact at Sun. However, after a series of misunderstandings...
View ArticleToorcon, Cold Boot Attacks, and geli
I spent this past weekend in San Diego to check out Toorcon 10. The presentations varied greatly in quality but there were a number that were memorable. Alexander Sotirov presented "How To Impress...
View ArticleLawrence Stewart gets his commit bit
A week or so ago I sponsored Lawrence Stewart for a commit bit. He is extremely knowledgeable about congestion control protocols and is actually working on adding modules for several new ones to...
View ArticleSubversion project branches for freebsd.org
The long anticipated availability of project branches in the main FreeBSD svn repository is finally here. Prior to this week the only widely accepted option that was really available for this was...
View ArticleXen support in FreeBSD
In response to one poster's question, yes Xen support for 32-bit SMP guests is in -CURRENT.For further details see the FreeBSD Xen wiki page. If you have questions please subscribe to the freebsd-xen...
View ArticleFlow Caching - a solution to IP performance problems?
Not too long ago Qing Li committed ECMP (equal-cost multi-path) support to FreeBSD. One particular application of this is to use FreeBSD as a load-balancer by setting it up as a gateway between a large...
View Articleper-cpu flow caching in FreeBSD
Along with some other experimental work (multiple transmit queues - which have just now made it in to HEAD) I now have per-cpu flow caches in a personal svn...
View ArticleUpdates
Its been a while. Flowtable support made it by default in to 8.0. One oversight that come up shortly afterwards is that it adversely impacts performance for systems with many routing prefixes to a...
View ArticleZFS, ARC, page cache, and 1970s buffer tuning
Some time ago Pawel Dawidek ported Sun's ZFS to FreeBSD. ZFS has many interesting features. One of the more problematic features on general purpose systems is the disk block caching in the ARC...
View ArticleHow txg_sync_thread dispatches writes - ZFS I/O notes part 1/4
The point of these notes is to document how the txg_sync_thread ends up calling dbuf_sync_indirect and dbuf_sync_leaf for dirty buffers (dbufs). As far as I can tell all indirect blocks depend on their...
View ArticleHow writes are scheduled for I/O - ZFS I/O notes part 2/4
The function zfs_write is the vnode operation for writes in ZFS. Since we're really only interested in ZFS we'll skip how a write system call reaches this point.vnodeops_t *zfs_fvnodeops;const...
View ArticleUnderstanding ZIO - ZFS I/O notes part 3/4
Each zio references associated dirty data, disk blocks, spa, vdev, associated transforms (e.g. compression, encryption, etc). The operations that will be executed are defined by a bitmask indicating...
View ArticleExecution of a zio_write zio - ZFS notes part 4/4
This is a whirlwind tour through the execution of each of the stages of a zio created by zio_write. It should help to give a rudimentary feeling for how the pipeline execution of a typical write I/O...
View ArticleWhen Optimized Out Isn't - Developer and Bug Submitter's Guide
A quick guide to debugging "optimized" code for the assembly phobic developer and bug submitterWith clang generated code one will frequently see that a variable has its "value optimized out". This...
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