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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mreitz@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="jgGkrZYTCkyVdcxzy8kr5Bky8Ted2Bb2i" Received-SPF: pass client-ip=63.128.21.124; envelope-from=mreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/15 02:10:02 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-1.019, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, fam@euphon.net, libvir-list@redhat.com, qemu-devel@nongnu.org, armbru@redhat.com, stefanha@redhat.com, den@openvz.org, jsnow@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --jgGkrZYTCkyVdcxzy8kr5Bky8Ted2Bb2i Content-Type: multipart/mixed; boundary="P2Zz7Z81tiseYjkhHzQyWl23xCi0Zv39o" --P2Zz7Z81tiseYjkhHzQyWl23xCi0Zv39o Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 14.10.20 18:39, Vladimir Sementsov-Ogievskiy wrote: > 14.10.2020 19:30, Max Reitz wrote: >> On 14.10.20 17:22, Vladimir Sementsov-Ogievskiy wrote: >>> 14.10.2020 15:51, Max Reitz wrote: >>>> On 12.10.20 19:43, Andrey Shinkevich wrote: >>>>> If the flag BDRV_REQ_PREFETCH was set, pass it further to the >>>>> COR-driver to skip unneeded reading. It can be taken into account for >>>>> the COR-algorithms optimization. That check is being made during the >>>>> block stream job by the moment. >>>>> >>>>> Signed-off-by: Andrey Shinkevich >>>>> --- >>>>> =C2=A0=C2=A0 block/copy-on-read.c | 13 +++++++++---- >>>>> =C2=A0=C2=A0 block/io.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0 |=C2=A0 3 ++- >>>>> =C2=A0=C2=A0 2 files changed, 11 insertions(+), 5 deletions(-) >>>>> >>>>> diff --git a/block/copy-on-read.c b/block/copy-on-read.c >>>>> index b136895..278a11a 100644 >>>>> --- a/block/copy-on-read.c >>>>> +++ b/block/copy-on-read.c >>>>> @@ -148,10 +148,15 @@ static int coroutine_fn >>>>> cor_co_preadv_part(BlockDriverState *bs, >>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0 } >>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >>>>> =C2=A0=C2=A0 -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ret =3D bdrv= _co_preadv_part(bs->file, offset, n, qiov, >>>>> qiov_offset, >>>>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 local_flags); >>>>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (ret < 0) { >>>>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 r= eturn ret; >>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (!!(flags & BDRV_REQ_P= REFETCH) & >>>> >>>> How about dropping the double negation and using a logical && >>>> instead of >>>> the binary &? >>>> >>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 != (local_flags & BDRV_REQ_COPY_ON_READ)) { >>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /= * Skip non-guest reads if no copy needed */ >>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } else { >>>> >>>> Hm.=C2=A0 I would have just written the negated form >>>> >>>> (!(flags & BDRV_REQ_PREFETCH) || (local_flags & BDRV_REQ_COPY_ON_READ)= ) >>>> >>>> and put the =E2=80=9Cskip=E2=80=9D comment above that condition. >>>> >>>> (Since local_flags is initialized to flags, it can be written as a >>>> single comparison, but that=E2=80=99s a matter of taste and I=E2=80=99= m not going to >>>> recommend either over the other: >>>> >>>> ((local_flags & (BDRV_REQ_PREFETCH | BDRV_REQ_COPY_ON_READ)) !=3D >>>> BDRV_REQ_PREFETCH) >>>> >>>> ) >>>> >>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 r= et =3D bdrv_co_preadv_part(bs->file, offset, n, qiov, >>>>> qiov_offset, >>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0 local_flags); >>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 i= f (ret < 0) { >>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0 return ret; >>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >>>>> =C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 o= ffset +=3D n; >>>>> diff --git a/block/io.c b/block/io.c >>>>> index 11df188..bff1808 100644 >>>>> --- a/block/io.c >>>>> +++ b/block/io.c >>>>> @@ -1512,7 +1512,8 @@ static int coroutine_fn >>>>> bdrv_aligned_preadv(BdrvChild *child, >>>>> =C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 max_bytes =3D ROUND_UP(MA= X(0, total_bytes - offset), align); >>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (bytes <=3D max_bytes && byte= s <=3D max_transfer) { >>>>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ret =3D bdrv_driver_pread= v(bs, offset, bytes, qiov, >>>>> qiov_offset, 0); >>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ret =3D bdrv_driver_pread= v(bs, offset, bytes, qiov, >>>>> qiov_offset, >>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 flags & bs->supported_r= ead_flags); >>> >>> >>> When BDRV_REQ_PREFETCH is passed, qiov may be (and generally should be) >>> NULL. This means, that we can't just drop the flag when call the driver >>> that doesn't support it. >> >> True. :/ >> >>> Actually, if driver doesn't support the PREFETCH flag we should do >>> nothing. >> >> Hm.=C2=A0 But at least in the case of COR, PREFETCH is not something tha= t can >> be optimized to be a no-op (unless the COR is a no-op); it still denotes >> a command that must be executed. >> >> So if we can=E2=80=99t pass it to the driver, I don=E2=80=99t think we s= hould do >> nothing, but to return an error.=C2=A0 Or maybe we could even assert tha= t it >> isn=E2=80=99t set for drivers that don=E2=80=99t support it, because at = least right now >> such a case would just be a bug. >=20 > Hmm. Reasonable.. >=20 > So, let me summarize the cases: >=20 > 1. bdrv_co_preadv(.. , PREFETCH | COR) >=20 > =C2=A0 In this case generic layer should handle both flags and pass flags= =3D0 > to driver >=20 > 2. bdrv_co_preadv(.., PREFETCH) >=20 > 2.1 driver supporst PREFETCH > =C2=A0 =C2=A0 OK, pass PREFETCH to driver, no problems >=20 > 2.2 driver doesn't support PREFETCH >=20 > =C2=A0 We can just abort() here, as the only source of PREFETCH without C= OR > would be > =C2=A0 stream job driver, which must read from COR filter. >=20 > =C2=A0 More generic solution is to allocate temporary buffer (at least if > qiov is NULL) > =C2=A0 and call underlying driver .preadv with flags=3D0 on that temporar= y > buffer. But > =C2=A0 just abort() is simpler and should work for now. Agreed. 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