From: Paulina Szubarczyk <paulinaszubarczyk@gmail.com>
To: David Vrabel <dvrabel@cantab.net>
Cc: sstabellini@kernel.org, wei.liu2@citrix.com,
George.Dunlap@eu.citrix.com, ian.jackson@eu.citrix.com,
P.Gawkowski@ii.pw.edu.pl, anthony.perard@citrix.com,
xen-devel@lists.xenproject.org, roger.pau@citrix.com
Subject: Re: [PATCH RESEND 3/4] qdisk, hw/block/xen_disk: Perform grant copy instead of grant map.
Date: Wed, 01 Jun 2016 09:52:58 +0200 [thread overview]
Message-ID: <1464767578.8602.19.camel@localhost> (raw)
In-Reply-To: <0235970d-7dc4-4f39-3f88-483f9065aed1@cantab.net>
On Tue, 2016-05-31 at 10:37 +0100, David Vrabel wrote:
> On 31/05/2016 05:44, Paulina Szubarczyk wrote:
> > Grant copy operation is divided into two phases different for
> > 'read' and 'write' operation.
> >
> > For a 'read' operation the flow is as follow:
> > 1. allocate local buffers for all the segments contained in
> > a request.
>
> Allocating buffers page-by-page looks sub-optimal to me. Why not
> allocate one large buffer for the whole request?
I thought about caching the pages and reuse them if there are more request.
I did the change in the next patch 4/4.
> > 2. fill the request io vectors with the buffers' addresses
> > 3. invoke read operation by qemu device
> > 4. in the completition call grant copy
> > 5. free the buffers
> >
> > Function 'ioreq_read_init' implements 1. and 2. step. It is called
> > instead of 'ioreq_map' in 'ioreq_runio_qemu_aio'. Then the function
> > 'ioreq_runio_qemu_aio' continues withouth changes performing step 3.
> > Steps 4. and 5. are called in the callback function
> > 'qemu_aio_complete'. The ioreq_read' function is implemented for
> > step 4 which calls the new function 'xc_gnttab_copy_grant' presented
> > in the other part of the patch.
> >
> > For a 'write' operation steps 4. happens before step 2.. First data
> > are copied from calling guest domains and then qemu operates on
> > them.
> > ---
> > hw/block/xen_disk.c | 185 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 185 insertions(+)
> >
> > diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
> > index 3b7882e..43cd9c9 100644
> > --- a/hw/block/xen_disk.c
> > +++ b/hw/block/xen_disk.c
> > @@ -284,6 +284,154 @@ err:
> > return -1;
> > }
> >
> > +
> > +static void* get_buffer(void) {
> > + void *buf;
> > +
> > + buf = mmap(NULL, 1 << XC_PAGE_SHIFT, PROT_READ | PROT_WRITE,
> > + MAP_SHARED | MAP_ANONYMOUS, -1, 0);
> > +
> > + if (unlikely(buf == MAP_FAILED))
> > + return NULL;
> > +
> > + return buf;
> > +}
> > +
> > +static int free_buffer(void* buf) {
> > + return munmap(buf, 1 << XC_PAGE_SHIFT);
>
> I would make this void and assert() the munmap is successful since if
> buf is valid the munmap() cannot fail. This means...
>
> > +}
> > +
> > +static int free_buffers(void** page, int count)
>
> This can be void and...
>
> > +{
> > + int i, r = 0;
> > +
> > + for (i = 0; i < count; i++) {
> > +
> > + if(free_buffer(page[i]))
> > + r = 1;
> > +
> > + page[i] = NULL;
> > + }
> > +
> > + return r;
> > +}
> > +
> > +static int ioreq_write(struct ioreq *ioreq)
> > +{
> > + XenGnttab gnt = ioreq->blkdev->xendev.gnttabdev;
> > + uint16_t domids[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> > + uint32_t refs[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> > + uint32_t offset[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> > + uint32_t len[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> > + void *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> > + int i, count = 0, rc, r;
> > + /* Copy the data for write operation from guest grant pages addressed by
> > + * domids, refs, offset, len to local buffers.
> > + *
> > + * Bufferes are then mapped to the pending request for further
> > + * completition.
> > + */
> > +
> > + if (ioreq->v.niov == 0) {
> > + r = 0; goto out;
> > + }
> > +
> > + count = ioreq->v.niov;
> > + for (i = 0; i < count; i++) {
> > + domids[i] = ioreq->domids[i];
> > + refs[i] = ioreq->refs[i];
> > + offset[i] = ioreq->req.seg[i].first_sect * ioreq->blkdev->file_blk;
> > + len[i] = (ioreq->req.seg[i].last_sect - ioreq->req.seg[i].first_sect + 1)
> > + * ioreq->blkdev->file_blk;
> > + pages[i] = get_buffer();
> > +
> > + if(!pages[i]) {
> > + xen_be_printf(&ioreq->blkdev->xendev, 0,
> > + "failed to alloc page, errno %d \n", errno);
> > + r = 1; goto out;
> > + }
> > + }
> > + rc = xc_gnttab_copy_grant(gnt, count, domids, refs, pages, offset, len, 1);
> > +
> > + if(rc) {
> > + xen_be_printf(&ioreq->blkdev->xendev, 0,
> > + "failed to copy data for write %d \n", rc);
> > +
> > + if(free_buffers(ioreq->page, ioreq->v.niov)) {
> > + xen_be_printf(&ioreq->blkdev->xendev, 0,
> > + "failed to free page, errno %d \n", errno);
> > + }
> > + r = 1; goto out;
> > + }
> > +
> > + for (i = 0; i < ioreq->v.niov; i++) {
> > + ioreq->page[i] = pages[i];
> > + ioreq->v.iov[i].iov_base += (uintptr_t)pages[i];
> > + }
> > +
> > + r = 0;
> > +out:
> > + return r;
> > +}
> > +
> > +static int ioreq_read_init(struct ioreq *ioreq)
> > +{
> > + int i;
> > +
> > + if (ioreq->v.niov == 0) {
> > + return 0;
> > + }
> > +
> > + for (i = 0; i < ioreq->v.niov; i++) {
> > + ioreq->page[i] = get_buffer();
> > + if(!ioreq->page[i]) {
> > + return -1;
> > + }
> > + ioreq->v.iov[i].iov_base += (uintptr_t)ioreq->page[i];
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +static int ioreq_read(struct ioreq *ioreq)
> > +{
> > + XenGnttab gnt = ioreq->blkdev->xendev.gnttabdev;
> > + uint16_t domids[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> > + uint32_t refs[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> > + uint32_t offset[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> > + uint32_t len[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> > + void *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> > + int i, count = 0, rc;
> > +
> > + /* Copy the data from local buffers to guest grant pages addressed by
> > + * domids, refs, offset on the completition of read operation.
> > + */
> > +
> > + if (ioreq->v.niov == 0) {
> > + return 0;
> > + }
> > +
> > + count = ioreq->v.niov;
> > + for (i = 0; i < count; i++) {
> > + domids[i] = ioreq->domids[i];
> > + refs[i] = ioreq->refs[i];
> > + offset[i] = ioreq->req.seg[i].first_sect * ioreq->blkdev->file_blk;
> > + len[i] = (ioreq->req.seg[i].last_sect - ioreq->req.seg[i].first_sect + 1)
> > + * ioreq->blkdev->file_blk;
> > + pages[i] = ioreq->v.iov[i].iov_base;
> > + }
>
> You can build the ops for read/write at the same time using the same
> code as the only difference is the direction.
> > +
> > + rc = xc_gnttab_copy_grant(gnt, count, domids, refs, pages, offset, len, 0);
> > +
> > + if(rc) {
> > + xen_be_printf(&ioreq->blkdev->xendev, 0,
> > + "failed to copy data to guest %d \n", rc);
> > + return -1;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > static int ioreq_runio_qemu_aio(struct ioreq *ioreq);
> >
> > static void qemu_aio_complete(void *opaque, int ret)
> > @@ -313,6 +461,22 @@ static void qemu_aio_complete(void *opaque, int ret)
> > }
> >
> > ioreq->status = ioreq->aio_errors ? BLKIF_RSP_ERROR : BLKIF_RSP_OKAY;
> > +
> > + switch(ioreq->req.operation) {
> > + case BLKIF_OP_READ:
> > + if(ioreq_read(ioreq)) {
> > + xen_be_printf(&ioreq->blkdev->xendev, 0,
> > + "failed to copy read data to guest\n");
>
> You need to report the failure back to the frontend.
>
> > + }
>
> Need a comment here since you're deliberating missing the "break".
>
> > + case BLKIF_OP_WRITE:
> > + if(free_buffers(ioreq->page, ioreq->v.niov)) {
>
> ...you don't need to consider errors here (see comment on free_buffer()
> above).
Thank you for all the above remarks I will correct the code.
Paulina
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next prev parent reply other threads:[~2016-06-01 7:53 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-31 4:44 [PATCH RESEND 0/4] qemu-qdisk: Replace grant map by grant copy Paulina Szubarczyk
2016-05-31 4:44 ` [PATCH RESEND 1/4] libs, gnttab, libxc: Interface for grant copy operation Paulina Szubarczyk
2016-05-31 9:25 ` David Vrabel
2016-06-01 7:45 ` Paulina Szubarczyk
2016-06-01 11:22 ` David Vrabel
2016-06-01 11:42 ` Paulina Szubarczyk
2016-06-02 9:37 ` Roger Pau Monné
2016-06-06 14:47 ` Wei Liu
2016-05-31 4:44 ` [PATCH RESEND 2/4] qdisk, hw/block/xen_disk: Removal of grant mapping Paulina Szubarczyk
2016-05-31 9:26 ` David Vrabel
2016-06-02 9:41 ` Roger Pau Monné
2016-06-02 9:57 ` Paulina Szubarczyk
2016-06-02 10:22 ` David Vrabel
2016-05-31 4:44 ` [PATCH RESEND 3/4] qdisk, hw/block/xen_disk: Perform grant copy instead of grant map Paulina Szubarczyk
2016-05-31 9:37 ` David Vrabel
2016-06-01 7:52 ` Paulina Szubarczyk [this message]
2016-06-01 11:15 ` David Vrabel
2016-06-02 13:47 ` Roger Pau Monné
2016-05-31 4:44 ` [PATCH RESEND 4/4] qemu-xen-dir/hw/block: Cache local buffers used in grant copy Paulina Szubarczyk
2016-06-02 14:19 ` Roger Pau Monné
2016-06-07 13:13 ` Paulina Szubarczyk
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