Re: [PATCH 1/6] block: add blk_io_plug_call() API

From: Stefan Hajnoczi <stefanha@redhat.com>
To: Eric Blake <eblake@redhat.com>
Cc: qemu-devel@nongnu.org, xen-devel@lists.xenproject.org,
	"Julia Suvorova" <jusual@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	"Stefano Garzarella" <sgarzare@redhat.com>,
	"Kevin Wolf" <kwolf@redhat.com>, "Fam Zheng" <fam@euphon.net>,
	"Philippe Mathieu-Daudé" <philmd@linaro.org>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	qemu-block@nongnu.org, "Paul Durrant" <paul@xen.org>,
	"Anthony Perard" <anthony.perard@citrix.com>,
	"Aarushi Mehta" <mehta.aaru20@gmail.com>,
	"Hanna Reitz" <hreitz@redhat.com>
Subject: Re: [PATCH 1/6] block: add blk_io_plug_call() API
Date: Tue, 23 May 2023 11:47:38 -0400	[thread overview]
Message-ID: <20230523154738.GD96478@fedora> (raw)
In-Reply-To: <7bsmwvpfmf6kelaxv32p6nhqcx2f2um2vqhvhu6uw5cooztrhe@oijddrxc2ysx>

[-- Attachment #1: Type: text/plain, Size: 1869 bytes --]

On Thu, May 18, 2023 at 07:04:52PM -0500, Eric Blake wrote:
> On Wed, May 17, 2023 at 06:10:17PM -0400, Stefan Hajnoczi wrote:
> > Introduce a new API for thread-local blk_io_plug() that does not
> > traverse the block graph. The goal is to make blk_io_plug() multi-queue
> > friendly.
> > 
> > Instead of having block drivers track whether or not we're in a plugged
> > section, provide an API that allows them to defer a function call until
> > we're unplugged: blk_io_plug_call(fn, opaque). If blk_io_plug_call() is
> > called multiple times with the same fn/opaque pair, then fn() is only
> > called once at the end of the function - resulting in batching.
> > 
> > This patch introduces the API and changes blk_io_plug()/blk_io_unplug().
> > blk_io_plug()/blk_io_unplug() no longer require a BlockBackend argument
> > because the plug state is now thread-local.
> > 
> > Later patches convert block drivers to blk_io_plug_call() and then we
> > can finally remove .bdrv_co_io_plug() once all block drivers have been
> > converted.
> > 
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > ---
> 
> > +++ b/block/plug.c
> > +
> > +/**
> > + * blk_io_plug_call:
> > + * @fn: a function pointer to be invoked
> > + * @opaque: a user-defined argument to @fn()
> > + *
> > + * Call @fn(@opaque) immediately if not within a blk_io_plug()/blk_io_unplug()
> > + * section.
> > + *
> > + * Otherwise defer the call until the end of the outermost
> > + * blk_io_plug()/blk_io_unplug() section in this thread. If the same
> > + * @fn/@opaque pair has already been deferred, it will only be called once upon
> > + * blk_io_unplug() so that accumulated calls are batched into a single call.
> > + *
> > + * The caller must ensure that @opaque is not be freed before @fn() is invoked.
> 
> s/be //

Will fix, thanks!

Stefan

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]