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From: boqun.feng@gmail.com
To: Michael Kelley <mikelley@microsoft.com>
Cc: "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
	"linux-input@vger.kernel.org" <linux-input@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
	KY Srinivasan <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Wei Liu <wei.liu@kernel.org>, Jiri Kosina <jikos@kernel.org>,
	Benjamin Tissoires <benjamin.tissoires@redhat.com>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	"James E.J. Bottomley" <jejb@linux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>
Subject: Re: [RFC 11/11] scsi: storvsc: Support PAGE_SIZE larger than 4K
Date: Thu, 23 Jul 2020 09:51:49 +0800
Message-ID: <20200723015149.GE35358@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net> (raw)
In-Reply-To: <MW2PR2101MB1052B072CA85F82B74BE799FD7760@MW2PR2101MB1052.namprd21.prod.outlook.com>

On Thu, Jul 23, 2020 at 12:13:07AM +0000, Michael Kelley wrote:
> From: Boqun Feng <boqun.feng@gmail.com> Sent: Monday, July 20, 2020 6:42 PM
> > 
> > Hyper-V always use 4k page size (HV_HYP_PAGE_SIZE), so when
> > communicating with Hyper-V, a guest should always use HV_HYP_PAGE_SIZE
> > as the unit for page related data. For storvsc, the data is
> > vmbus_packet_mpb_array. And since in scsi_cmnd, sglist of pages (in unit
> > of PAGE_SIZE) is used, we need convert pages in the sglist of scsi_cmnd
> > into Hyper-V pages in vmbus_packet_mpb_array.
> > 
> > This patch does the conversion by dividing pages in sglist into Hyper-V
> > pages, offset and indexes in vmbus_packet_mpb_array are recalculated
> > accordingly.
> > 
> > Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> > ---
> >  drivers/scsi/storvsc_drv.c | 27 +++++++++++++++++++++------
> >  1 file changed, 21 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
> > index fb41636519ee..c54d25f279bc 100644
> > --- a/drivers/scsi/storvsc_drv.c
> > +++ b/drivers/scsi/storvsc_drv.c
> > @@ -1561,7 +1561,7 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct
> > scsi_cmnd *scmnd)
> >  	struct hv_host_device *host_dev = shost_priv(host);
> >  	struct hv_device *dev = host_dev->dev;
> >  	struct storvsc_cmd_request *cmd_request = scsi_cmd_priv(scmnd);
> > -	int i;
> > +	int i, j, k;
> >  	struct scatterlist *sgl;
> >  	unsigned int sg_count = 0;
> >  	struct vmscsi_request *vm_srb;
> > @@ -1569,6 +1569,8 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct
> > scsi_cmnd *scmnd)
> >  	struct vmbus_packet_mpb_array  *payload;
> >  	u32 payload_sz;
> >  	u32 length;
> > +	int subpage_idx = 0;
> > +	unsigned int hvpg_count = 0;
> > 
> >  	if (vmstor_proto_version <= VMSTOR_PROTO_VERSION_WIN8) {
> >  		/*
> > @@ -1643,23 +1645,36 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct
> > scsi_cmnd *scmnd)
> >  	payload_sz = sizeof(cmd_request->mpb);
> > 
> >  	if (sg_count) {
> > -		if (sg_count > MAX_PAGE_BUFFER_COUNT) {
> > +		hvpg_count = sg_count * (PAGE_SIZE / HV_HYP_PAGE_SIZE);
> 
> The above calculation doesn't take into account the offset in the
> first sglist or the overall length of the transfer, so the value of hvpg_count
> could be quite a bit bigger than it needs to be.  For example, with a 64K
> page size and an 8 Kbyte transfer size that starts at offset 60K in the
> first page, hvpg_count will be 32 when it really only needs to be 2.
> 
> The nested loops below that populate the pfn_array take the 
> offset into account when starting, so that's good.  But it will potentially
> leave allocated entries unused.  Furthermore, the nested loops could
> terminate early when enough Hyper-V size pages are mapped to PFNs
> based on the length of the transfer, even if all of the last guest size
> page has not been mapped to PFNs.  Like the offset at the beginning of
> first guest size page in the sglist, there's potentially an unused portion
> at the end of the last guest size page in the sglist.
> 

Good point. I think we could calculate the exact hvpg_count as follow:

	hvpg_count = 0;
	cur_sgl = sgl;

	for (i = 0; i < sg_count; i++) {
		hvpg_count += HVPFN_UP(cur_sg->length)
		cur_sgl = sg_next(cur_sgl);
	}

> > +		if (hvpg_count > MAX_PAGE_BUFFER_COUNT) {
> > 
> > -			payload_sz = (sg_count * sizeof(u64) +
> > +			payload_sz = (hvpg_count * sizeof(u64) +
> >  				      sizeof(struct vmbus_packet_mpb_array));
> >  			payload = kzalloc(payload_sz, GFP_ATOMIC);
> >  			if (!payload)
> >  				return SCSI_MLQUEUE_DEVICE_BUSY;
> >  		}
> > 
> > +		/*
> > +		 * sgl is a list of PAGEs, and payload->range.pfn_array
> > +		 * expects the page number in the unit of HV_HYP_PAGE_SIZE (the
> > +		 * page size that Hyper-V uses, so here we need to divide PAGEs
> > +		 * into HV_HYP_PAGE in case that PAGE_SIZE > HV_HYP_PAGE_SIZE.
> > +		 */
> >  		payload->range.len = length;
> > -		payload->range.offset = sgl[0].offset;
> > +		payload->range.offset = sgl[0].offset & ~HV_HYP_PAGE_MASK;
> > +		subpage_idx = sgl[0].offset >> HV_HYP_PAGE_SHIFT;
> > 
> >  		cur_sgl = sgl;
> > +		k = 0;
> >  		for (i = 0; i < sg_count; i++) {
> > -			payload->range.pfn_array[i] =
> > -				page_to_pfn(sg_page((cur_sgl)));
> > +			for (j = subpage_idx; j < (PAGE_SIZE / HV_HYP_PAGE_SIZE); j++) {
> 
> In the case where PAGE_SIZE == HV_HYP_PAGE_SIZE, would it help the compiler
> eliminate the loop if local variable j is declared as unsigned?  In that case the test in the
> for statement will always be false.
> 

Good point! I did the following test:

test.c:

	int func(unsigned int input, int *arr)
	{
		unsigned int i;
		int result = 0;

		for (i = input; i < 1; i++)
			result += arr[i];

		return result;
	}

if I define i as "int", I got:

	0000000000000000 <func>:
	   0:	85 ff                	test   %edi,%edi
	   2:	7f 2c                	jg     30 <func+0x30>
	   4:	48 63 d7             	movslq %edi,%rdx
	   7:	f7 df                	neg    %edi
	   9:	45 31 c0             	xor    %r8d,%r8d
	   c:	89 ff                	mov    %edi,%edi
	   e:	48 8d 04 96          	lea    (%rsi,%rdx,4),%rax
	  12:	48 01 d7             	add    %rdx,%rdi
	  15:	48 8d 54 be 04       	lea    0x4(%rsi,%rdi,4),%rdx
	  1a:	66 0f 1f 44 00 00    	nopw   0x0(%rax,%rax,1)
	  20:	44 03 00             	add    (%rax),%r8d
	  23:	48 83 c0 04          	add    $0x4,%rax
	  27:	48 39 d0             	cmp    %rdx,%rax
	  2a:	75 f4                	jne    20 <func+0x20>
	  2c:	44 89 c0             	mov    %r8d,%eax
	  2f:	c3                   	retq   
	  30:	45 31 c0             	xor    %r8d,%r8d
	  33:	44 89 c0             	mov    %r8d,%eax
	  36:	c3                   	retq   

and when I define i as "unsigned int", I got:

	0000000000000000 <func>:
	   0:	85 ff                	test   %edi,%edi
	   2:	75 03                	jne    7 <func+0x7>
	   4:	8b 06                	mov    (%rsi),%eax
	   6:	c3                   	retq   
	   7:	31 c0                	xor    %eax,%eax
	   9:	c3                   	retq   

So clearly it helps, I will change this in the next version.

Regards,
Boqun

> > +				payload->range.pfn_array[k] =
> > +					page_to_hvpfn(sg_page((cur_sgl))) + j;
> > +				k++;
> > +			}
> >  			cur_sgl = sg_next(cur_sgl);
> > +			subpage_idx = 0;
> >  		}
> >  	}
> > 
> > --
> > 2.27.0
> 

  reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-21  1:41 [RFC 00/11] Hyper-V: " Boqun Feng
2020-07-21  1:41 ` [RFC 01/11] Drivers: hv: vmbus: Always use HV_HYP_PAGE_SIZE for gpadl Boqun Feng
2020-07-21 15:22   ` Wei Liu
2020-07-22 23:20     ` Boqun Feng
2020-07-21  1:41 ` [RFC 02/11] Drivers: hv: vmbus: Move __vmbus_open() Boqun Feng
2020-07-21 15:23   ` Wei Liu
2020-07-21  1:41 ` [RFC 03/11] Drivers: hv: vmbus: Introduce types of GPADL Boqun Feng
2020-07-22 23:25   ` Michael Kelley
2020-07-22 23:43     ` Boqun Feng
2020-07-22 23:56       ` Michael Kelley
2020-07-21  1:41 ` [RFC 04/11] Drivers: hv: Use HV_HYP_PAGE in hv_synic_enable_regs() Boqun Feng
2020-07-21  1:41 ` [RFC 05/11] Drivers: hv: vmbus: Move virt_to_hvpfn() to hyperv header Boqun Feng
2020-07-21  1:41 ` [RFC 06/11] hv: hyperv.h: Introduce some hvpfn helper functions Boqun Feng
2020-07-21  1:41 ` [RFC 07/11] hv_netvsc: Use HV_HYP_PAGE_SIZE for Hyper-V communication Boqun Feng
2020-07-21  1:41 ` [RFC 08/11] Input: hyperv-keyboard: Make ringbuffer at least take two pages Boqun Feng
2020-07-21  1:41 ` [RFC 09/11] HID: hyperv: " Boqun Feng
2020-07-22 23:36   ` Michael Kelley
2020-07-23  1:28     ` boqun.feng
2020-07-21  1:41 ` [RFC 10/11] Driver: hv: util: " Boqun Feng
2020-07-21  1:41 ` [RFC 11/11] scsi: storvsc: Support PAGE_SIZE larger than 4K Boqun Feng
2020-07-23  0:13   ` Michael Kelley
2020-07-23  1:51     ` boqun.feng [this message]
2020-07-23  2:26       ` Michael Kelley
2020-07-23  3:12         ` Boqun Feng

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