Re: [Qemu-block] [Qemu-devel] [PATCH 1/2] block/nvme: add support for write zeros

[Maxim Levitsky]

On Tue, 2019-08-27 at 18:22 -0400, John Snow wrote:
> Without a commit message, I have no real hope of reviewing this. I was
> CC'd, though, so I'll give it a blind shot.
> 
> We want to add write_zeroes support for block/nvme, but I can't really
> verify any of that is correct or working without a unit test, a spec, or
> some instructions to help me verify any of this does what it looks like
> it does.
> 
> On 8/25/19 3:15 AM, Maxim Levitsky wrote:
> > Signed-off-by: Maxim Levitsky <address@hidden>
> > ---
> >  block/nvme.c         | 72 +++++++++++++++++++++++++++++++++++++++++++-
> >  block/trace-events   |  1 +
> >  include/block/nvme.h | 19 +++++++++++-
> >  3 files changed, 90 insertions(+), 2 deletions(-)
> > 
> > diff --git a/block/nvme.c b/block/nvme.c
> > index 5be3a39b63..f8bd11e19a 100644
> > --- a/block/nvme.c
> > +++ b/block/nvme.c
> > @@ -111,6 +111,8 @@ typedef struct {
> >      uint64_t max_transfer;
> >      bool plugged;
> >  
> > +    bool supports_write_zeros;
> > +
> 
> I suppose the spelling of "zeroes" is not as established as I thought it
> was. Actually, what's worse is that the NVME writers apparently couldn't
> decide what to name it themselves either:
> 
> "Write Zeroes" has 23 hits.
> "Write Zeros" has just two, in Figure 114 for the Identify NS Data.
> 
> Oh, in QEMU we're not much better:
> 
> jhuston@probe (review) ~/s/qemu> git grep -i zeros | wc -l
> 265
> jhuston@probe (review) ~/s/qemu> git grep -i zeroes | wc -l
> 747
> 
> I'm going to suggest that we use 'zeroes' as the spelling here, to match
> the existing 'pwrite_zeroes', and then otherwise to match the NVME
> spec's usual spelling.
OK.


> 
> >      CoMutex dma_map_lock;
> >      CoQueue dma_flush_queue;
> >  
> > @@ -421,6 +423,7 @@ static void nvme_identify(BlockDriverState *bs, int 
> > namespace, Error **errp)
> >      NvmeIdNs *idns;
> >      NvmeLBAF *lbaf;
> >      uint8_t *resp;
> > +    uint16_t oncs;
> >      int r;
> >      uint64_t iova;
> >      NvmeCmd cmd = {
> > @@ -458,6 +461,9 @@ static void nvme_identify(BlockDriverState *bs, int 
> > namespace, Error **errp)
> >      s->max_transfer = MIN_NON_ZERO(s->max_transfer,
> >                            s->page_size / sizeof(uint64_t) * s->page_size);
> >  
> > +    oncs = le16_to_cpu(idctrl->oncs);
> > +    s->supports_write_zeros = (oncs & NVME_ONCS_WRITE_ZEROS) != 0;
> > +
> 
> For other reviewers: oncs is "Optional NVM Command Support".
> 
> I think it's better to say `!!(oncs & NVME_ONCS_WRITE_ZEROES)` to remove
> doubt over the width of the bitmask.
OK.
> 
> >      memset(resp, 0, 4096);
> >  
> >      cmd.cdw10 = 0;
> > @@ -470,6 +476,12 @@ static void nvme_identify(BlockDriverState *bs, int 
> > namespace, Error **errp)
> >      s->nsze = le64_to_cpu(idns->nsze);
> >      lbaf = &idns->lbaf[NVME_ID_NS_FLBAS_INDEX(idns->flbas)];
> >  
> > +    if (NVME_ID_NS_DLFEAT_WRITE_ZEROS(idns->dlfeat) &&
> > +            NVME_ID_NS_DLFEAT_READ_BEHAVIOR(idns->dlfeat) ==
> > +                    NVME_ID_NS_DLFEAT_READ_BEHAVIOR_ZEROS) {
> > +        bs->supported_write_flags |= BDRV_REQ_MAY_UNMAP;
> > +    }
> > +
> >      if (lbaf->ms) {
> >          error_setg(errp, "Namespaces with metadata are not yet supported");
> >          goto out;
> > @@ -764,6 +776,8 @@ static int nvme_file_open(BlockDriverState *bs, QDict 
> > *options, int flags,
> >      int ret;
> >      BDRVNVMeState *s = bs->opaque;
> >  
> > +    bs->supported_write_flags = BDRV_REQ_FUA;
> > +
> 
> Is this a related change?
Yes, because nvme write zero command supports this flag (always),
so since now the driver exposes write zeros, it tells the qemu that its
write zero command supports 'force unit access' flag.

> 
> >      opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
> >      qemu_opts_absorb_qdict(opts, options, &error_abort);
> >      device = qemu_opt_get(opts, NVME_BLOCK_OPT_DEVICE);
> > @@ -792,7 +806,6 @@ static int nvme_file_open(BlockDriverState *bs, QDict 
> > *options, int flags,
> >              goto fail;
> >          }
> >      }
> > -    bs->supported_write_flags = BDRV_REQ_FUA;
> >      return 0;
> >  fail:
> >      nvme_close(bs);
> > @@ -1086,6 +1099,60 @@ static coroutine_fn int 
> > nvme_co_flush(BlockDriverState *bs)
> >  }
> >  
> >  
> > +static coroutine_fn int nvme_co_pwrite_zeroes(BlockDriverState *bs,
> > +                                              int64_t offset,
> > +                                              int bytes,
> > +                                              BdrvRequestFlags flags)
> > +{
> > +    BDRVNVMeState *s = bs->opaque;
> > +    NVMeQueuePair *ioq = s->queues[1];
> 
> I think it'd be slick to name the queues, but that's not related to this
> patch.
Yea, but let do it in another patch.

> 
> > +    NVMeRequest *req;
> > +
> > +    uint32_t cdw12 = ((bytes >> s->blkshift) - 1) & 0xFFFF;
> > +
> > +    if (!s->supports_write_zeros) {
> > +        return -ENOTSUP;
> > +    }
> > +
> > +    NvmeCmd cmd = {
> > +        .opcode = NVME_CMD_WRITE_ZEROS,
> > +        .nsid = cpu_to_le32(s->nsid),
> > +        .cdw10 = cpu_to_le32((offset >> s->blkshift) & 0xFFFFFFFF),
> > +        .cdw11 = cpu_to_le32(((offset >> s->blkshift) >> 32) & 0xFFFFFFFF),
> > +    };
> > +
> > +    NVMeCoData data = {
> > +        .ctx = bdrv_get_aio_context(bs),
> > +        .ret = -EINPROGRESS,
> > +    };
> > +
> > +    if (flags & BDRV_REQ_MAY_UNMAP) {
> > +        cdw12 |= (1 << 25);
> > +    }
> > +
> > +    if (flags & BDRV_REQ_FUA) {
> > +        cdw12 |= (1 << 30);
> > +    }
> > +
> > +    cmd.cdw12 = cpu_to_le32(cdw12);
> > +
> > +    trace_nvme_write_zeros(s, offset, bytes, flags);
> > +    assert(s->nr_queues > 1);
> > +    req = nvme_get_free_req(ioq);
> > +    assert(req);
> > +
> > +    nvme_submit_command(s, ioq, req, &cmd, nvme_rw_cb, &data);
> > +
> > +    data.co = qemu_coroutine_self();
> > +    while (data.ret == -EINPROGRESS) {
> > +        qemu_coroutine_yield();
> > +    }
> > +
> > +    trace_nvme_rw_done(s, true, offset, bytes, data.ret);
> > +    return data.ret;
> > +}
> > +
> > +
> >  static int nvme_reopen_prepare(BDRVReopenState *reopen_state,
> >                                 BlockReopenQueue *queue, Error **errp)
> >  {
> > @@ -1190,6 +1257,9 @@ static BlockDriver bdrv_nvme = {
> >  
> >      .bdrv_co_preadv           = nvme_co_preadv,
> >      .bdrv_co_pwritev          = nvme_co_pwritev,
> > +
> > +    .bdrv_co_pwrite_zeroes    = nvme_co_pwrite_zeroes,
> > +
> >      .bdrv_co_flush_to_disk    = nvme_co_flush,
> >      .bdrv_reopen_prepare      = nvme_reopen_prepare,
> >  
> > diff --git a/block/trace-events b/block/trace-events
> > index 04209f058d..8209fbd0c7 100644
> > --- a/block/trace-events
> > +++ b/block/trace-events
> > @@ -149,6 +149,7 @@ nvme_submit_command_raw(int c0, int c1, int c2, int c3, 
> > int c4, int c5, int c6,
> >  nvme_handle_event(void *s) "s %p"
> >  nvme_poll_cb(void *s) "s %p"
> >  nvme_prw_aligned(void *s, int is_write, uint64_t offset, uint64_t bytes, 
> > int flags, int niov) "s %p is_write %d offset %"PRId64" bytes %"PRId64" 
> > flags %d niov %d"
> > +nvme_write_zeros(void *s, uint64_t offset, uint64_t bytes, int flags) "s 
> > %p offset %"PRId64" bytes %"PRId64" flags %d"
> 
> I was told once that we wanted trace events to match the name of the
> function they occurred within whenever possible.
> 
> Maybe we haven't really been very good about enforcing that.
> 
> Oh well.
I'll keep it as is, to keep it consistent with the rest of the tracing events.


> 
> >  nvme_qiov_unaligned(const void *qiov, int n, void *base, size_t size, int 
> > align) "qiov %p n %d base %p size 0x%zx align 0x%x"
> >  nvme_prw_buffered(void *s, uint64_t offset, uint64_t bytes, int niov, int 
> > is_write) "s %p offset %"PRId64" bytes %"PRId64" niov %d is_write %d"
> >  nvme_rw_done(void *s, int is_write, uint64_t offset, uint64_t bytes, int 
> > ret) "s %p is_write %d offset %"PRId64" bytes %"PRId64" ret %d"
> > diff --git a/include/block/nvme.h b/include/block/nvme.h
> > index 3ec8efcc43..1f5b406344 100644
> > --- a/include/block/nvme.h
> > +++ b/include/block/nvme.h
> > @@ -653,12 +653,29 @@ typedef struct NvmeIdNs {
> >      uint8_t     mc;
> >      uint8_t     dpc;
> >      uint8_t     dps;
> > -    uint8_t     res30[98];
> > +
> > +    uint8_t     nmic;
> > +    uint8_t     rescap;
> > +    uint8_t     fpi;
> > +    uint8_t     dlfeat;
> > +
> > +    uint8_t     res30[94];
> 
> I wouldn't call this "res30" anymore, because now it starts at the 34th
> byte instead of the 30th.
Fixed.

> 
> >      NvmeLBAF    lbaf[16];
> >      uint8_t     res192[192];
> >      uint8_t     vs[3712];
> >  } NvmeIdNs;
> >  
> 
> Pre-existing, but what are any of these names supposed to mean?
> 
> (I imagine they match the spec, but where?...)
LBAF - this is LBA format, which basically tells you the hardware sector
size, and metadata size for each sector. On high end drives its is possible
to choose one of such formats out of this table when formatting an namespace.
vs = vendor specific.

Note that the whole struct (and other structs here) are very outdated since 
fields are
added all the time in newer spec revisions. This is the joy of maintaining the 
separate
driver, in addition to the kernel driver which is more or less up to date.

> 
> Leaving me some breadcrumbs would greatly reduce the time it takes
> someone who doesn't already know NVME to review this, and I suspect
> you've looked them up recently, so leaving little notes in the cover
> letter at least for relevant sections is very nice for hardware spec
> patches like this.
> 
> > +
> > +/*Deallocate Logical Block Features*/
> 
> ah. "dlfeat" --> "Deallocate Logical (Block) Features".
> 
> From here:
> 
> NVME Express 1.3, Figure 114: Identify - Identify Namespace Data
> Structure, NVM Command Set Specific
> 
> > +#define NVME_ID_NS_DLFEAT_GUARD_CRC(dlfeat)       ((dlfeat) & 0x10)
> 
> Not used in this patch?
Yes, but I prefer at least to document all the bits in the field, even 
if not used.

> 
> > +#define NVME_ID_NS_DLFEAT_WRITE_ZEROS(dlfeat)     ((dlfeat) & 0x08)
> > +
> > +#define NVME_ID_NS_DLFEAT_READ_BEHAVIOR(dlfeat)     ((dlfeat) & 0x7)
> > +#define NVME_ID_NS_DLFEAT_READ_BEHAVIOR_UNDEFINED   0
> > +#define NVME_ID_NS_DLFEAT_READ_BEHAVIOR_ZEROS       1
> > +#define NVME_ID_NS_DLFEAT_READ_BEHAVIOR_ONES        2
> > +
> > +
> >  #define NVME_ID_NS_NSFEAT_THIN(nsfeat)      ((nsfeat & 0x1))
> >  #define NVME_ID_NS_FLBAS_EXTENDED(flbas)    ((flbas >> 4) & 0x1)
> >  #define NVME_ID_NS_FLBAS_INDEX(flbas)       ((flbas & 0xf))
> > 
> 
> Seems good otherwise, but I didn't trace the actual execution of the new
> command too far -- I'll assume it works. :)

Best regards,
        Maxim Levitsky