Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

2008-02-20 Thread Neil Brown
On Tuesday February 19, [EMAIL PROTECTED] wrote: > On Mon, Feb 18, 2008 at 04:24:27PM +0300, Michael Tokarev wrote: > > First, I still don't understand why in God's sake barriers are "working" > > while regular cache flushes are not. Almost no consumer-grade hard drive > > supports write barriers,

Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

2008-02-20 Thread Neil Brown
On Monday February 18, [EMAIL PROTECTED] wrote: > > > I'll put it even more strongly. My experience is that disabling write > cache plus disabling barriers is often much faster than enabling both > barriers and write cache enabled, when doing metadata intensive > operations, as long as you have

Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

2008-02-20 Thread Ric Wheeler
Jeremy Higdon wrote: On Tue, Feb 19, 2008 at 09:16:44AM +1100, David Chinner wrote: On Mon, Feb 18, 2008 at 04:24:27PM +0300, Michael Tokarev wrote: First, I still don't understand why in God's sake barriers are "working" while regular cache flushes are not. Almost no consumer-grade hard drive

Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

2008-02-19 Thread Andi Kleen
> My complaint about having to support them within dm when more than one > device is involved is because any efficiencies disappear: you can't send > further I/O to any one device until all the other devices have completed > their barrier (or else later I/O to that device could overtake the > barri

Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

2008-02-18 Thread Michael Tokarev
Jeremy Higdon wrote: [] > I'll put it even more strongly. My experience is that disabling write > cache plus disabling barriers is often much faster than enabling both > barriers and write cache enabled, when doing metadata intensive > operations, as long as you have a drive that is good at CTQ/NC

Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

2008-02-18 Thread Jeremy Higdon
On Tue, Feb 19, 2008 at 09:16:44AM +1100, David Chinner wrote: > On Mon, Feb 18, 2008 at 04:24:27PM +0300, Michael Tokarev wrote: > > First, I still don't understand why in God's sake barriers are "working" > > while regular cache flushes are not. Almost no consumer-grade hard drive > > supports w

Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

2008-02-18 Thread David Chinner
On Tue, Feb 19, 2008 at 02:56:43AM +, Alasdair G Kergon wrote: > On Tue, Feb 19, 2008 at 09:16:44AM +1100, David Chinner wrote: > > Surely any hardware that doesn't support barrier > > operations can emulate them with cache flushes when they receive a > > barrier I/O from the filesystem >

Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

2008-02-18 Thread Alasdair G Kergon
On Tue, Feb 19, 2008 at 09:16:44AM +1100, David Chinner wrote: > Surely any hardware that doesn't support barrier > operations can emulate them with cache flushes when they receive a > barrier I/O from the filesystem My complaint about having to support them within dm when more than one devic

Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

2008-02-18 Thread Alasdair G Kergon
On Mon, Feb 18, 2008 at 08:52:10AM -0500, Ric Wheeler wrote: > I understand that. Most of the time, dm or md devices are composed of > uniform components which will uniformly support (or not) the cache flush > commands used by barriers. As a dm developer, it's "almost none of the time" because

Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

2008-02-18 Thread David Chinner
On Mon, Feb 18, 2008 at 04:24:27PM +0300, Michael Tokarev wrote: > First, I still don't understand why in God's sake barriers are "working" > while regular cache flushes are not. Almost no consumer-grade hard drive > supports write barriers, but they all support regular cache flushes, and > the la

Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

2008-02-18 Thread Ric Wheeler
Michael Tokarev wrote: Ric Wheeler wrote: Alasdair G Kergon wrote: On Fri, Feb 15, 2008 at 03:20:10PM +0100, Andi Kleen wrote: On Fri, Feb 15, 2008 at 04:07:54PM +0300, Michael Tokarev wrote: I wonder if it's worth the effort to try to implement this. My personal view (which seems to be in t

Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

2008-02-18 Thread Michael Tokarev
Ric Wheeler wrote: > Alasdair G Kergon wrote: >> On Fri, Feb 15, 2008 at 03:20:10PM +0100, Andi Kleen wrote: >>> On Fri, Feb 15, 2008 at 04:07:54PM +0300, Michael Tokarev wrote: I wonder if it's worth the effort to try to implement this. >> >> My personal view (which seems to be in the minorit

Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

2008-02-18 Thread Ric Wheeler
Alasdair G Kergon wrote: On Fri, Feb 15, 2008 at 03:20:10PM +0100, Andi Kleen wrote: On Fri, Feb 15, 2008 at 04:07:54PM +0300, Michael Tokarev wrote: I wonder if it's worth the effort to try to implement this. My personal view (which seems to be in the minority) is that it's a waste of our de

Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

2008-02-15 Thread Alan Cox
> And don't RH distributions install with LVM by default these days? > For those it should be the standard case too on all systems with > only a single disk. Yes - I make a point of turning it off ;) Alan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a

Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

2008-02-15 Thread Andi Kleen
On Fri, Feb 15, 2008 at 02:12:29PM +, Alasdair G Kergon wrote: > On Fri, Feb 15, 2008 at 03:20:10PM +0100, Andi Kleen wrote: > > On Fri, Feb 15, 2008 at 04:07:54PM +0300, Michael Tokarev wrote: > > > I wonder if it's worth the effort to try to implement this. > > My personal view (which seems

Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

2008-02-15 Thread Alasdair G Kergon
On Fri, Feb 15, 2008 at 03:20:10PM +0100, Andi Kleen wrote: > On Fri, Feb 15, 2008 at 04:07:54PM +0300, Michael Tokarev wrote: > > I wonder if it's worth the effort to try to implement this. My personal view (which seems to be in the minority) is that it's a waste of our development time *except*